Display panel and information processing device

ABSTRACT

A novel display panel that can be used as a reflective display panel in an environment with strong external light and as a self-luminous display panel in a dim environment, for example and that has low power consumption and is highly convenient or reliable is provided. The display panel includes a pixel and a substrate that supports the pixel. The pixel includes a first display element (e.g., a reflective liquid crystal element) that includes a reflective film having an opening as a first conductive film and a second display element (e.g., an organic EL element) that emits light to the opening.

TECHNICAL FIELD

One embodiment of the present invention relates to a display panel, aninformation processing device, or a semiconductor device.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of one embodiment of theinvention disclosed in this specification and the like relates to anobject, a method, or a manufacturing method. In addition, one embodimentof the present invention relates to a process, a machine, manufacture,or a composition of matter. Specifically, examples of the technicalfield of one embodiment of the present invention disclosed in thisspecification include a semiconductor device, a display device, alight-emitting device, a power storage device, a memory device, a methodfor driving any of them, and a method for manufacturing any of them.

BACKGROUND ART

A liquid crystal display device in which a light-condensing means and apixel electrode are provided on the same surface side of a substrate anda region transmitting visible light in the pixel electrode is providedto overlap with an optical axis of the light-condensing means, and aliquid crystal display device which includes an anisotropiclight-condensing means having a condensing direction X and anon-condensing direction Y that is along a longitudinal direction of aregion transmitting visible light in the pixel electrode are known(Patent Document 1).

REFERENCE Patent Document [Patent Document 1] Japanese Published PatentApplication No. 2011-191750 DISCLOSURE OF INVENTION

An object of one embodiment of the present invention is to provide anovel display panel that is highly convenient or reliable. Anotherobject of one embodiment of the present invention is to provide a novelinformation processing device that is highly convenient or reliable.Another object of one embodiment of the present invention is to providea novel display panel, a novel information processing device, or a novelsemiconductor device.

Note that the description of these objects does not disturb theexistence of other objects. In one embodiment of the present invention,there is no need to achieve all the objects. Other objects will beapparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

(1) One embodiment of the present invention is a display panel thatincludes a pixel and a substrate.

The substrate is configured to support the pixel.

The pixel includes a first display element and a second display elementthat has a region overlapping with the first display element.

The first display element includes a reflective film that reflectsexternal light and is configured to control transmission of the externallight.

The reflective film includes an opening.

The second display element is configured to emit light to the openingand a region overlapping with the opening.

(2) Another embodiment of the present invention is the above displaypanel in which the first display element includes a liquid crystallayer, a first conductive film, and a second conductive film.

The second display element includes a layer containing a luminescentmaterial, a third conductive film, and a fourth conductive film.

The reflective film serves as the first conductive film.

The area of the opening is greater than or equal to 5% and less than orequal to 20% of the area of the first conductive film.

The second display element is configured to emit light to a regionhaving a shape overlapping with the opening.

The display panel of one embodiment of the present invention includesthe pixel and the substrate supporting the pixel. The pixel includes thefirst display element (e.g., a reflective liquid crystal element) thatincludes the reflective film having the opening as the first conductivefilm, and the second display element (e.g., an organic EL element) thatemits light to the opening.

With this structure, the display panel can be used, for example, as areflective display panel in an environment with strong external light.Specifically, an image with high contrast can be favorably displayed inan environment with bright external light. The display panel can beused, for example, as a self-luminous display panel in a dim environmentto display an image favorably. Thus, a novel display panel that has lowpower consumption and is highly convenient or reliable can be provided.

(3) Another embodiment of the present invention is the above displaypanel that includes a first scan line and a first signal lineintersecting with the first scan line.

The pixel includes a first pixel circuit.

The first pixel circuit is electrically connected to the first scan lineand the first signal line.

The first pixel circuit is configured to drive the first displayelement.

(4) Another embodiment of the present invention is the above displaypanel that includes a second scan line and a second signal lineintersecting with the second scan line.

The pixel includes a second pixel circuit.

The second pixel circuit is electrically connected to the second scanline and the second signal line.

The second pixel circuit is configured to drive the second displayelement.

The display panel of one embodiment of the present invention includesthe first pixel circuit configured to drive the first display element orthe second pixel circuit configured to drive the second display element.With this structure, the first display element or the second displayelement can be selectively used to perform display. Thus, a noveldisplay panel that has low power consumption and is highly convenient orreliable can be provided.

(5) Another embodiment of the present invention is the above displaypanel in which the first pixel circuit includes a transistor.

The transistor is configured to reduce current flowing in an off statemore than a transistor including amorphous silicon as a semiconductor.

In the display panel of one embodiment of the present invention, thefirst pixel circuit configured to drive the first display elementincludes the transistor that can reduce current flowing in an off state.With this structure, the frequency of supplying a selection signal tothe first pixel circuit can be reduced while flickers of display arereduced. Alternatively, power consumption can be reduced. Thus, a noveldisplay panel that is highly convenient or reliable can be provided.

(6) One embodiment of the present invention is an information processingdevice that includes an arithmetic device and an input/output device.

The arithmetic device is configured to receive positional informationand supply image information and control information.

The input/output device is configured to supply the positionalinformation and receive the image information and the controlinformation.

The input/output device includes a display portion that displays theimage information and an input portion that supplies the positionalinformation.

The display portion includes the above display panel.

The input portion is configured to detect the position of a pointer andsupply positional information determined in accordance with the positionof the pointer.

The arithmetic device is configured to determine the moving speed of thepointer in accordance with the positional information.

The arithmetic device is configured to determine the contrast orbrightness of image information in accordance with the moving speed ofthe pointer.

The above information processing device of one embodiment of the presentinvention includes the input/output device that supplies positionalinformation and receives image information and the arithmetic devicethat receives the positional information and supplies the imageinformation. The arithmetic device determines the contrast or brightnessof image information in accordance with the moving speed of the pointer.With this structure, eyestrain on a user caused when the displayposition of image information is moved can be reduced, that is,eye-friendly display can be achieved. Thus, a novel informationprocessing device that is highly convenient or reliable can be provided.

(7) Another embodiment of the present invention is the above informationprocessing device in which the input portion includes at least one of akeyboard, a hardware button, a pointing device, a touch sensor, anilluminance sensor, an imaging device, an audio input device, aviewpoint input device, and a pose detection device.

Thus, the information processing device can have low power consumptionand excellent visibility even in a bright place. Thus, a novelinformation processing device that is highly convenient or reliable canbe provided.

Although the block diagram attached to this specification showscomponents classified by their functions in independent blocks, it isdifficult to classify actual components according to their functionscompletely and it is possible for one component to have a plurality offunctions.

In this specification, the terms “source” and “drain” of a transistorinterchange with each other depending on the polarity of the transistoror the levels of potentials applied to the terminals. In general, in ann-channel transistor, a terminal to which a lower potential is appliedis called a source, and a terminal to which a higher potential isapplied is called a drain. Furthermore, in a p-channel transistor, aterminal to which a lower potential is applied is called a drain, and aterminal to which a higher potential is applied is called a source. Inthis specification, although connection relation of the transistor isdescribed assuming that the source and the drain are fixed in some casesfor convenience, actually, the names of the source and the draininterchange with each other depending on the relation of the potentials.

Note that in this specification, a “source” of a transistor means asource region that is part of a semiconductor film functioning as anactive layer or a source electrode connected to the semiconductor film.Similarly, a “drain” of the transistor means a drain region that is partof the semiconductor film or a drain electrode connected to thesemiconductor film. A “gate” means a gate electrode.

Note that in this specification, a state in which transistors areconnected to each other in series means, for example, a state in whichonly one of a source and a drain of a first transistor is connected toonly one of a source and a drain of a second transistor. In addition, astate in which transistors are connected to each other in parallel meansa state in which one of a source and a drain of a first transistor isconnected to one of a source and a drain of a second transistor and theother of the source and the drain of the first transistor is connectedto the other of the source and the drain of the second transistor.

In this specification, the term “connection” means electrical connectionand corresponds to a state where current, voltage, or a potential can besupplied or transmitted. Accordingly, a connection state means not onlya state of direct connection but also a state of indirect connectionthrough a circuit element such as a wiring, a resistor, a diode, or atransistor that allows current, voltage, or a potential to be suppliedor transmitted.

In this specification, even when different components are connected toeach other in a circuit diagram, there is actually a case where oneconductive film has functions of a plurality of components such as acase where part of a wiring serves as an electrode. The term“connection” also means such a case where one conductive film hasfunctions of a plurality of components.

In addition, in this specification, one of a first electrode and asecond electrode of a transistor refers to a source electrode and theother refers to a drain electrode.

One embodiment of the present invention can provide a novel displaypanel that is highly convenient or reliable. Alternatively, a novelinformation processing device that is highly convenient or reliable canbe provided. Alternatively, a novel display panel, a novel informationprocessing device, or a novel semiconductor device can be provided.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the effects listed above. Other effects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top view illustrating a structure of a display panel of oneembodiment.

FIG. 2 is a top view illustrating a structure of a pixel arranged in adisplay panel of one embodiment.

FIG. 3 is a cross-sectional view illustrating a structure of a displaypanel of one embodiment.

FIGS. 4A and 4B are cross-sectional views illustrating a structure of afirst display portion of a display panel of one embodiment.

FIG. 5 is a cross-sectional view illustrating a structure of a seconddisplay portion of a display panel of one embodiment.

FIG. 6 is a cross-sectional view illustrating a structure of a displaypanel of one embodiment.

FIGS. 7A and 7B are cross-sectional views illustrating a structure of afirst display portion of a display panel of one embodiment.

FIG. 8 is a cross-sectional view illustrating a structure of a seconddisplay portion of a display panel of one embodiment.

FIGS. 9A to 9D illustrate structures of a transistor of one embodiment.

FIGS. 10A to 10C illustrate structures of a transistor of oneembodiment.

FIG. 11 illustrates a structure of an input/output device of oneembodiment.

FIG. 12A is a block diagram and FIG. 12B is a projection view eachillustrating a structure of an information processing device of oneembodiment.

FIGS. 13A and 13B are block diagrams each illustrating a structure of adisplay portion of one embodiment and FIGS. 13C and 13D are each acircuit diagram illustrating a structure of a display portion of oneembodiment.

FIGS. 14A and 14B are flow charts each illustrating a program of oneembodiment.

FIG. 15 is a schematic diagram illustrating image information of oneembodiment.

FIG. 16A is a cross-sectional view and FIGS. 16B and 16C are circuitdiagrams each illustrating a structure of a semiconductor device of oneembodiment.

FIG. 17 is a block diagram illustrating a structure of a CPU of oneembodiment.

FIG. 18 is a circuit diagram illustrating a structure of a memoryelement of one embodiment.

FIGS. 19A to 19H each illustrate a structure of an electronic device ofone embodiment.

FIG. 20 is a cross-sectional view illustrating a structure of a displaypanel of one embodiment.

FIGS. 21A and 21B are schematic diagrams each illustrating a displayingmethod and a structure of a display panel of Example.

FIG. 22 is a top view illustrating a structure of a pixel of a displaypanel of Example.

FIGS. 23A and 23B illustrate a method for manufacturing a display panelof Example.

FIGS. 24A to 24D are photographs showing display states of a displaypanel of Example.

FIGS. 25A and 25B are photographs showing display states of displaypanels of Example.

BEST MODE FOR CARRYING OUT THE INVENTION

The display panel of one embodiment of the present invention includes apixel and a substrate supporting the pixel. The pixel includes a firstdisplay element (e.g., a reflective liquid crystal element) thatincludes a reflective film having an opening as a first conductive filmand a second display element (e.g., an organic EL element) that emitslight to the opening.

With this structure, the display panel can be used, for example, as areflective display panel in an environment with strong external lightand as a self-luminous display panel in a dim environment. Thus, a noveldisplay panel that has low power consumption and is highly convenient orreliable can be provided.

Embodiments will be described in detail with reference to the drawings.Note that the present invention is not limited to the followingdescription, and it is easily understood by those skilled in the artthat various changes and modifications can be made without departingfrom the spirit and scope of the present invention. Therefore, thepresent invention should not be construed as being limited to thedescription in the following embodiments. In the structures of theinvention described below, the same portions or portions having similarfunctions are denoted by the same reference numerals in differentdrawings, and description of such portions is not repeated.

Embodiment 1

In this embodiment, the structure of a display panel of one embodimentof the present invention will be described with reference to FIG. 1,FIG. 2, FIG. 3, FIGS. 4A and 4B, FIG. 5, FIG. 6, FIGS. 7A and 7B, andFIG. 8.

<Structure Example 1 of Display Panel>

FIG. 1 is a top view illustrating the structure of the display panel ofone embodiment of the present invention.

FIG. 2 is a top view illustrating the structure of a pixel in thedisplay panel of one embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating structures of the displaypanel of one embodiment of the present invention taken along the cuttingplane lines X1-X2, X3-X4, and X5-X6 in FIG. 1.

FIG. 4A is a cross-sectional view illustrating structures of a firstdisplay portion 700E of the display panel of one embodiment of thepresent invention taken along the cutting plane lines X1-X2, X3-X4, andX5-X6 in FIG. 1. FIG. 4B is a cross-sectional view illustrating thestructure of a transistor.

FIG. 5 is a cross-sectional view illustrating structures of a seconddisplay portion 500E of the display panel of one embodiment of thepresent invention taken along the cutting plane lines X1-X2, X3-X4, andX5-X6 in FIG. 1.

The display panel described in this embodiment includes a pixel 702E anda substrate 710 (see FIG. 1, FIG. 2, and FIG. 3). Note that a sub-pixel702EB, a sub-pixel 702EG, or a sub-pixel 702ER can be used in the pixel702E.

The substrate 710 has a function of supporting the pixel 702E (see FIG.3). The substrate 710 has a region overlapping with the pixel 702E.

The pixel 702E includes a first display element 750EB and a seconddisplay element 550EB that includes a region overlapping with the firstdisplay element 750EB (see FIG. 2 and FIG. 3).

The first display element 750EB includes a reflective film (a firstconductive film 751EB) that reflects external light and has a functionof controlling transmission of external light. The reflective film (thefirst conductive film 751EB) has an opening 751H.

The second display element 550EB has a function of emitting light to theopening 751H and a region overlapping with the opening 751H.

The first display element 750EB includes a liquid crystal layer 753, thefirst conductive film 751E, and a second conductive film 752 (see FIGS.4A and 4B).

The second display element 550EB includes a layer 553E containing aluminescent material, a third conductive film 551EB, and a fourthconductive film 552 (see FIG. 5).

The reflective film has a function as the first conductive film 751E.The area of the opening 751H is, for example, greater than or equal to5% and less than or equal to 20%, preferably 10% of that of the firstconductive film 751E.

The second display element 550EB has a function of emitting light to aregion with a shape substantially overlapping with the opening 751H.Note that the region with a shape substantially overlapping with theopening 751H includes a region overlapping with the opening 751H and aregion not overlapping with the opening 751H. The area of the region notoverlapping with the opening 751H is less than or equal to 20%,preferably less than or equal to 10% of the area of the regionoverlapping with the opening 751H.

Specifically, the area of the light-emitting region of the seconddisplay element 550EB is greater than or equal to 0.5 times and lessthan 1.5 times, preferably greater than or equal to 0.8 times and lessthan 1.2 times, more preferably greater than or equal to 0.9 times andless than 1.1 times as large as that of the opening 751H.

The above display panel includes the sub-pixel 702EB and the substrate710 that supports the sub-pixel 702EB. The sub-pixel 702EB includes thefirst display element 750EB (e.g., a reflective liquid crystal element)including a reflective film having the opening 751H as the firstconductive film 751E and the second display element 550EB (e.g., anorganic EL element) that emits light to the opening 751H.

With this structure, the display panel can be used, for example, as areflective display panel in an environment with strong external light,and specifically, an image with high contrast can be favorably displayedin an environment with bright external light. The display panel can beused, for example, as a self-luminous display panel in a dim environmentto display an image favorably. Thus, the novel display panel that haslow power consumption and is highly convenient or reliable can beprovided.

<Structure>

The display panel of one embodiment of the present invention includesthe first display portion 700E, the second display portion 500E, and abonding layer 535 (see FIG. 1 and FIG. 3).

<<First Display Portion 700E>>

The first display portion 700E includes a pixel portion, a wiringportion, a source driver circuit portion SD1, a gate driver circuitportion GD1, and a terminal portion (see FIG. 1 and FIGS. 4A and 4B).

The first display portion 700E further includes the substrate 710, asubstrate 770, a structure body KB1, the liquid crystal layer 753, asealant 730, and an optical film 770P.

The substrate 770 includes a region overlapping with the substrate 710.

The sealant 730 has a function of bonding the substrate 710 and thesubstrate 770 to each other.

The liquid crystal layer 753 is provided in a region surrounded by thesubstrate 710, the substrate 770, and the sealant 730.

The structure body KB1 is provided between the substrate 710 and thesubstrate 770. The structure body KB1 has a function of keeping apredetermined distance between the substrate 710 and the substrate 770.

<<Pixel Portion>>

The pixel portion includes the pixel 702E, a light-blocking film BM, theinsulating film 771, an insulating film 721A, an insulating film 721B,and an insulating film 728.

For example, a plurality of sub-pixels can be used in the pixel 702E.Specifically, the sub-pixel 702EB, which displays a blue image, thesub-pixel 702EG, which displays a green image, the sub-pixel 702ER,which displays a red image, and the like can be used. In addition, asub-pixel that displays a white image, a sub-pixel that displays ayellow image, or the like can be used.

For example, when the area of the pixel that displays a blue image islarger than that of the pixel that displays an image of a color otherthan blue, a white image can favorably be displayed.

<<Pixel>>

The pixel 702E includes the first display element 750EB, a coloring filmCF1, and a pixel circuit.

<<First Display Element 750EB>>

For example, a display element having a function of controllingtransmission or reflection of light can be used as the first displayelement 750EB. For example, a combined structure of a polarizing plateand a liquid crystal element or a MEMS shutter display element can beused.

Specifically, a liquid crystal element that can be driven by any of thefollowing driving methods can be used: an in-plane switching (IPS) mode,a twisted nematic (TN) mode, a fringe field switching (FFS) mode, anaxially symmetric aligned micro-cell (ASM) mode, an opticallycompensated birefringence (OCB) mode, a ferroelectric liquid crystal(FLC) mode, an antiferroelectric liquid crystal (AFLC) mode, and thelike.

Alternatively, a liquid crystal element that can be driven by a drivingmethod such as a vertical alignment (VA) mode, specifically, amulti-domain vertical alignment (MVA) mode, a patterned verticalalignment (PVA) mode, or an ASV mode can be used.

For example, thermotropic liquid crystal, low-molecular liquid crystal,high-molecular liquid crystal, polymer dispersed liquid crystal,ferroelectric liquid crystal, or anti-ferroelectric liquid crystal canbe used. These liquid crystal materials exhibit a cholesteric phase, asmectic phase, a cubic phase, a chiral nematic phase, an isotropicphase, or the like depending on conditions. Alternatively, a liquidcrystal material which exhibits a blue phase can be used.

For example, the first display element 750EB includes the liquid crystallayer 753 containing a liquid crystal material and the first conductivefilm 751E and the second conductive film 752 disposed such that anelectric field which controls the orientation of the liquid crystalmaterial can be applied.

A conductive material can be used for the first conductive film 751E.

For example, a material used for the wiring portion can be used for thefirst conductive film 751E or the second conductive film 752.

For example, a material that reflects light incident from the liquidcrystal layer 753 side can be used for the first conductive film 751E.This allows the first display element 750EB to serve as a reflectiveliquid crystal element.

For example, a conductive film whose surface has projections anddepressions can be used for the first conductive film 751E. In thatcase, incident light can be reflected in various directions so that awhite image can be displayed.

For example, a conductive material that transmits visible light can beused for the second conductive film 752.

For example, a conductive oxide or an indium-containing conductive oxidecan be used for the second conductive film 752. Alternatively, a metalfilm that is thin enough to transmit light can be used as the secondconductive film 752.

Specifically, indium oxide, indium tin oxide, indium zinc oxide, zincoxide, or zinc oxide to which gallium is added can be used for thesecond conductive film 752.

<<Opening 751H>>

In the first display portion 700F, the opening 751H is formed in thefirst conductive film 751E. Part of light incident from the substrate710 passes through the opening 751H and can be emitted from thesubstrate 770.

The area of the opening 751H is preferably greater than or equal to 5%and less than or equal to 20%, more preferably 10% of that of the firstconductive film 751E.

The opening 751H may have a polygonal shape, a quadrangular shape, anelliptical shape, a circular shape, or a cross shape, for example.

<<Coloring Film CF1>>

The coloring film CF1 includes a region overlapping with the firstdisplay element 750EB and has a function of transmitting light of apredetermined color. The coloring film CF1 can be used as a colorfilter, for example.

For example, the coloring film CF1, which transmits blue light, can beused in the sub-pixel 702EB. A coloring film that transmits green lightcan be used in the sub-pixel 702EG. A coloring film that transmits redlight can be used in the sub-pixel 702ER. Furthermore, a coloring filmthat transmits white light and a coloring film that transmits yellowlight can be used in sub-pixels for displaying a variety of colors.

<<Light-Blocking Film BM>>

The light-blocking film BM has an opening in a region overlapping withthe sub-pixel 702EB.

A material that prevents light transmission can be used for thelight-blocking film BM, in which case the light-blocking film BM servesas a black matrix, for example.

<<Pixel Circuit>>

A transistor ME1 a capacitor C1, or the like can be used in the pixelcircuit.

The transistor ME1 includes a semiconductor film 718 and a conductivefilm 704 including a region overlapping with the semiconductor film 718(see FIG. 4B). The transistor ME1 further includes a conductive film712A and a conductive film 712B.

Note that the conductive film 712A has one of a function as a sourceelectrode and a function as a drain electrode, and the conductive film712B has the other. The conductive film 704 serves as a gate electrode,and an insulating film 706 serves as a gate insulating film.

The transistor ME1 can be, for example, a transistor having a functionof reducing current flowing in an off state more than a transistor usingamorphous silicon as a semiconductor. With this structure, the frequencyof supplying a selection signal to a first pixel circuit can be reducedwhile flickers of display are reduced. Alternatively, power consumptioncan be reduced. Specifically, a transistor described in Embodiment 2 or3 can be used as the transistor ME1.

The capacitor C1 includes the conductive film 712A and a conductive filmincluding a region overlapping with the conductive film 712A (see FIG.4A).

Note that the conductive film 712A is electrically connected to thefirst conductive film 751E.

<<Insulating Film>>

The insulating film 771 is disposed between the liquid crystal layer 753and the light-blocking film BM or between the liquid crystal layer 753and the coloring film CF1.

A material having a function of inhibiting diffusion of impurities intothe liquid crystal layer 753 from the light-blocking film BM, thecoloring film CF1, and the like can be used for the insulating film 771.

The insulating film 721B includes a region overlapping with theconductive film 704 and a region overlapping with the semiconductor film718.

The insulating film 721A is provided between the semiconductor film 718and the insulating film 721B (see FIGS. 4A and 4B).

<<Insulating Film 728>>

The insulating film 728 is provided between the insulating film 721B andthe liquid crystal layer 753.

The insulating film 728 can eliminate level differences caused byvarious structures underlying the insulating film 728. Thus, the liquidcrystal layer 753 can have a uniform thickness.

For example, an insulating inorganic material, an insulating organicmaterial, or an insulating composite material containing an inorganicmaterial or an organic material can be used for the insulating film 728(see FIG. 4A).

Specifically, an inorganic oxide film, an inorganic nitride film, aninorganic oxynitride film, or a material obtained by stacking any ofthese films can be used for the insulating film 728.

Specifically, for the insulating film 728, polyester, polyolefin,polyamide, polyimide, polycarbonate, polysiloxane, an acrylic resin, orthe like, or a layered material or a composite material of a pluralityof kinds of resins selected from these can be used. Alternatively, aphotosensitive material may be used.

<<Source Driver Circuit Portion SD1>>

For example, an integrated circuit can be used in the source drivercircuit portion SD1. Specifically, an integrated circuit formed over asilicon substrate can be used (see FIG. 1).

For example, a chip on glass (COG) method can be used to mount thesource driver circuit portion SD1 on a pad provided over the substrate710. Specifically, an anisotropic conductive film can be used to mountthe integrated circuit on the pad. Note that the pad is electricallyconnected to the pixel circuit.

<<Gate Driver Circuit Portion GD1>>

For example, a transistor ME2 can be used in the gate driver circuitportion GD1 (see FIGS. 4A and 4B).

For example, the transistor described in Embodiment 2 or Embodiment 3can be used as the transistor ME2.

For example, a semiconductor film that can be formed through the sameprocess as the semiconductor film 718 included in the transistor ME1 canbe used in the transistor ME2.

Note that the transistor ME2 can have the same structure as thetransistor ME1. Alternatively, the transistor ME2 may have a structuredifferent from that of the transistor ME1.

<<Conductive Film 720>>

The conductive film 720 includes a region overlapping with thesemiconductor film 718. In other words, the semiconductor film 718 isprovided between the conductive film 720 and the conductive film 704.This can improve the characteristics or reliability of the transistorME1 or the transistor ME2.

The conductive film 720 can be used for a second gate electrode of thetransistor ME2. The conductive film 720 can be regarded as part of thetransistor ME1 or the transistor ME2.

For example, a wiring through which the potential equal to that of theconductive film 704 can be supplied can be electrically connected to theconductive film 720.

For example, a material used for the wiring portion can be used for theconductive film 720. Specifically, conductive oxide, indium-containingconductive oxide, indium oxide, indium tin oxide, indium zinc oxide,indium zinc gallium oxide, zinc oxide, zinc oxide to which gallium isadded, or the like can be used for the conductive film 720.

<<Wiring Portion, Terminal Portion>>

The wiring portion includes a signal line 711, and the terminal portionincludes a connection electrode 719 (see FIG. 4A).

The signal line 711 is electrically connected to the connectionelectrode 719. Part of the signal line 711 can be used for theconnection electrode 719.

The connection electrode 719 is electrically connected to a flexibleprinted substrate FPC1 with the use of, for example, a conductive memberACF1.

A conductive material can be used for the signal line 711 and theconnection electrode 719.

For example, an inorganic conductive material, an organic conductivematerial, a metal material, or a conductive ceramic material can be usedfor the signal line 711 or the connection electrode 719.

Specifically, a metal element selected from aluminum, gold, platinum,silver, copper, chromium, tantalum, titanium, molybdenum, tungsten,nickel, iron, cobalt, palladium, and manganese, or the like can be usedfor the signal line 711 or the connection electrode 719. Alternatively,an alloy containing any of the above-described metal elements, or thelike can be used for the signal line 711 or the connection electrode719. In particular, an alloy of copper and manganese is suitably used inmicrofabrication with the use of a wet etching method.

Specifically, a two-layer structure in which a titanium film is stackedover an aluminum film, a two-layer structure in which a titanium film isstacked over a titanium nitride film, a two-layer structure in which atungsten film is stacked over a titanium nitride film, a two-layerstructure in which a tungsten film is stacked over a tantalum nitridefilm or a tungsten nitride film, a three-layer structure in which atitanium film, an aluminum film, and a titanium film are stacked in thisorder, or the like can be employed for the signal line 711 or theconnection electrode 719.

Specifically, a conductive oxide such as indium oxide, indium tin oxide,indium zinc oxide, zinc oxide, or zinc oxide to which gallium is addedcan be used for the signal line 711 or the connection electrode 719.

Specifically, a film including graphene or graphite can be used for thesignal line 711 or the connection electrode 719.

For example, a film including graphene oxide is formed and is subjectedto reduction, so that a film including graphene can be formed. As areducing method, a method using heat, a method using a reducing agent,or the like can be employed.

Specifically, a conductive polymer can be used for the signal line 711or the connection electrode 719.

<<Conductive Member ACF1>>

For example, solder, a conductive paste, or an anisotropic conductivefilm can be used for the conductive member ACF1.

Specifically, conductive particles, a material that disperses particles,and the like can be used for the conductive member ACF1.

For example, a spherical, columnar, or filler particle with a size ofgreater than or equal to 1 μm and less than or equal to 200 μm,preferably greater than or equal to 3 μm and less than or equal to 150μm can be used.

For example, a particle covered with a conductive material containingnickel, gold, or the like can be used.

Specifically, a particle containing polystyrene, an acrylic resin,titanium oxide, or the like can be used.

For example, synthetic rubber, a thermosetting resin, or a thermoplasticresin can be used for the material that disperses particles.

Thus, the flexible printed substrate FPC1 can be electrically connectedto the connection electrode 719 with the use of particles.

<<Substrate 710>>

A light-transmitting material is used for the substrate 710.Alternatively, a material that is reduced in thickness by a polishingmethod can be used for the substrate 710.

For example, a layered material of a base 710A and an insulating film710B can be used for the substrate 710. The insulating film 710B has afunction of inhibiting diffusion of impurities contained in the base710A or impurities from the outside.

A material having heat resistance high enough to withstand heattreatment in the manufacturing process can be used for the substrate710.

For example, a large-sized glass substrate having any of the followingsizes can be used as the substrate 710: the 6th generation (1500 mm×1850mm), the 7th generation (1870 mm×2200 mm), the 8th generation (2200mm×2400 mm), the 9th generation (2400 mm×2800 mm), and the 10thgeneration (2950 mm×3400 mm). Thus, a large-sized display device can bemanufactured.

For the substrate 710, an organic material, an inorganic material, acomposite material of an organic material and an inorganic material, orthe like can be used. For example, an inorganic material such as glass,ceramic, or metal can be used for the substrate 710.

Specifically, non-alkali glass, soda-lime glass, potash glass, crystalglass, quartz, sapphire, or the like can be used for the substrate 710.Specifically, an inorganic oxide film, an inorganic nitride film, aninorganic oxynitride film, or the like can be used for the substrate710. For example, a silicon oxide film, a silicon nitride film, asilicon oxynitride film, or an alumina film can be used for thesubstrate 710. For example, SUS or aluminum can be used for thesubstrate 710.

For example, a single crystal semiconductor substrate or apolycrystalline semiconductor substrate of silicon or silicon carbide, acompound semiconductor substrate of silicon germanium or the like, or anSOI substrate can be used as the substrate 710. Thus, a semiconductorelement can be provided over the substrate 710.

For example, an organic material such as a resin, a resin film, orplastic can be used for the substrate 710. Specifically, a resin film orresin plate of polyester, polyolefin, polyamide, polyimide,polycarbonate, an acrylic resin, or the like can be used for thesubstrate 710.

For example, a composite material formed by attaching a metal plate, athin glass plate, or a film of an inorganic material to a resin film orthe like can be used for the substrate 710. For example, a compositematerial formed by dispersing a fibrous or particulate metal, glass,inorganic material, or the like into a resin film can be used for thesubstrate 710. For example, a composite material formed by dispersing afibrous or particulate resin, organic material, or the like into aninorganic material can be used for the substrate 710.

Furthermore, a single-layer material or a layered material in which aplurality of layers are stacked can be used for the substrate 710. Forexample, a layered material in which a base, an insulating film thatprevents diffusion of impurities contained in the base, and the like arestacked can be used for the substrate 710. Specifically, a layeredmaterial in which glass and one or a plurality of films that areselected from a silicon oxide layer, a silicon nitride layer, a siliconoxynitride layer, and the like and that prevent diffusion of impuritiescontained in the glass are stacked can be used for the substrate 710.Alternatively, a layered material in which a resin and a film forpreventing diffusion of impurities that penetrate the resin, such as asilicon oxide film, a silicon nitride film, and a silicon oxynitridefilm are stacked can be used for the substrate 710.

Specifically, a resin film, a resin plate, a stack, or the like ofpolyester, polyolefin, polyamide, polyimide, polycarbonate, an acrylicresin, or the like can be used for the substrate 710.

Specifically, a material including polyester, polyolefin, polyamide(e.g., nylon or aramid), polyimide, polycarbonate, polyurethane, anacrylic resin, an epoxy resin, a resin having a siloxane bond such assilicone, or the like can be used for the substrate 710.

Specifically, polyethylene terephthalate (PET), polyethylene naphthalate(PEN), polyethersulfone (PES), acrylic, or the like can be used for thesubstrate 710.

Alternatively, paper, wood, or the like can be used for the substrate710.

For example, a flexible substrate can be used as the substrate 710.

Note that a transistor, a capacitor, or the like can be directly formedon the flexible substrate. Alternatively, a transistor, a capacitor, orthe like formed on a process substrate having heat resistance can betransferred to a flexible substrate.

<<Substrate 770>>

A light-transmitting material can be used for the substrate 770.

For example, a material that can be used for the substrate 710 can beused for the substrate 770.

<<Sealant 730>>

For the sealant 730, an inorganic material, an organic material, acomposite material of an inorganic material and an organic material, orthe like can be used.

For example, an organic material such as a thermally fusible resin or acurable resin can be used for the sealant 730.

For example, an organic material such as a reactive curable adhesive, alight curable adhesive, a thermosetting adhesive, and/or an anaerobicadhesive can be used for the sealant 730.

Specifically, an adhesive containing an epoxy resin, an acrylic resin, asilicone resin, a phenol resin, a polyimide resin, an imide resin, apolyvinyl chloride (PVC) resin, a polyvinyl butyral (PVB) resin, and anethylene vinyl acetate (EVA) resin, or the like can be used for thesealant 730.

<<Optical Film 770P>>

The substrate 770 is located between the optical film 770P and theliquid crystal layer 753. The optical film 770P includes a regionoverlapping with the first display element 750EB.

For example, a polarizing plate, a retardation plate, a diffusing film,a condensing film, or the like can be used as the optical film 770P.

A hard coat layer that prevents damage can be used as the optical film,for example.

<<Second Display Portion 500E>>

The second display portion 500E includes a pixel portion, a wiringportion, a source driver circuit portion SD2, a gate driver circuitportion GD2, and a terminal portion (see FIG. 1 and FIG. 5).

The second display portion 500E includes a substrate 510, an insulatingfilm 570, a structure body KB2, and a bonding layer 530.

The second display portion 500E further includes a coloring film CF2 andan insulating film 571.

The second display portion 500E further includes an insulating film521A, an insulating film 521B, a partition wall 528A, and an insulatingfilm 528B.

The insulating film 570 includes a region overlapping with the substrate510.

The bonding layer 530 has a function of bonding the substrate 510 andthe insulating film 570 to each other.

The structure body KB2 is provided between the substrate 510 and theinsulating film 570. The structure body KB2 has a function of keeping apredetermined distance between the substrate 510 and the insulating film570.

<<Pixel Portion>>

The pixel portion includes a pixel.

For example, a plurality of sub-pixels can be used in the pixel.Specifically, a sub-pixel that displays a blue image, a sub-pixel thatdisplays a green image, a sub-pixel that displays a red image, and thelike can be used. In addition, a sub-pixel that displays a white image,a sub-pixel that displays a yellow image, or the like can be used.

For example, when the area of the pixel that displays a blue image islarger than that of the pixel that displays an image of a color otherthan blue, a white image can be favorably displayed.

<<Pixel>>

The pixel includes the second display element 550EB, the coloring filmCF2, and a pixel circuit.

<<Second Display Element 550EB>>

The second display element 550EB has a function of emitting light to theopening 751H and a region overlapping with the opening 751H.

A region of the second display element 550EB that has a shapesubstantially overlapping with the opening 751H emits light (see FIG.2).

Any of a variety of light-emitting elements can be used as the seconddisplay element 550EB. For example, an organic electroluminescenceelement, an inorganic electroluminescence element, a light-emittingdiode, or the like can be used as the second display element 550EB.

For example, the third conductive film 551EB, the fourth conductive film552 including a region overlapping with the third conductive film 551EB,and the layer 553E containing a luminescent material between the thirdconductive film 551EB and the fourth conductive film 552 can be used inthe second display element 550EB (see FIG. 5).

For example, a luminescent organic compound can be used for the layer553E containing a luminescent material. Alternatively, quantum dots canbe used for the layer 553E containing a luminescent material. A stackformed to emit white light can be used as the layer 553E containing aluminescent material. Specifically, a stack of a layer containing aluminescent material containing a fluorescent material that emits bluelight and a layer containing a material that is other than a fluorescentmaterial and that emits green light and/or red light can be used as thelayer 553E containing a luminescent material.

For example, a material used for the wiring portion can be used for thethird conductive film 551EB or the fourth conductive film 552.

For example, a conductive material that reflects visible light can beused for the third conductive film 551EB.

For example, a conductive material that transmits visible light can beused for the fourth conductive film 552.

Specifically, conductive oxide, indium-containing conductive oxide,indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, zincoxide to which gallium is added, or the like can be used for the fourthconductive film 552.

Alternatively, a metal film that is thin enough to transmit light can beused as the fourth conductive film 552.

<<Coloring Film CF2>>

The coloring film CF2 is provided between the opening 751H of the firstconductive film 751E and the second display element 550EB.

The coloring film CF2 includes a region overlapping with the opening751H and the second display element 550EB and has a function oftransmitting light of a predetermined color. For example, a coloringfilm that transmits light passing through the coloring film CF1 can beused as the coloring film CF2. In that case, part of light emitted fromthe second display element 550EB that passes through the coloring filmCF2, the opening 751H, and the coloring film CF1 can be extracted to theoutside of a display panel. Note that a material having a function ofconverting the emitted light to a predetermined color light can be usedfor the coloring film CF2. Specifically, quantum dots can be used forthe coloring film CF2. Thus, display with high color purity can beachieved.

For example, the material that can be used for the coloring film CF1 canbe used for the coloring film CF2.

<<Pixel Circuit>>

A transistor ME3 or the like can be used in the pixel circuit.

For example, the structure that can be used for the transistor ME1 canbe used for the transistor ME3.

For example, the transistor described in Embodiment 2 or Embodiment 3can be used as the transistor ME3.

<<Insulating Film>>

The insulating film 571 is provided between the coloring film CF2 andthe bonding layer 530.

The insulating film 521B includes a region overlapping with theconductive film 504 and a region overlapping with the semiconductorfilm.

The insulating film 521A is provided between the semiconductor film andthe insulating film 521B (see FIG. 5).

<<Insulating Film 528B>>

The insulating film 528B can eliminate level differences caused byvarious structures underlying the insulating film 528B.

For example, the material that can be used for the insulating film 728can be used for the insulating film 528B.

<<Partition Wall 528A>>

The partition wall 528A has an opening in a region overlapping with thesecond display element 550EB. For example, an insulating material can beused for the partition wall 528A. In that case, the second displayelement 550EB can be insulated from another structure adjacent to thesecond display element 550EB. Alternatively, the shape of the seconddisplay element can be determined using the shape of the opening formedin the partition wall 528A.

For example, the material that can be used for the insulating film 528Bcan be used for the partition wall 528A.

<<Source Driver Circuit Portion SD2>>

For example, an integrated circuit can be used in the source drivercircuit portion SD2. Specifically, an integrated circuit formed over asilicon substrate can be used (see FIG. 1).

For example, a chip on glass (COG) method can be used to mount thesource driver circuit portion SD2 on a pad provided over the substrate510. Specifically, an anisotropic conductive film can be used to mountthe integrated circuit on the pad. Note that the pad is electricallyconnected to the pixel circuit.

<<Gate Driver Circuit Portion GD2>>

For example, a transistor ME4 can be used in the gate driver circuitportion GD2 (see FIG. 5).

For example, the transistor described in Embodiment 2 or Embodiment 3can be used as the transistor ME4.

For example, a semiconductor film that can be formed through the sameprocess as the semiconductor film included in the transistor ME3 can beused in the transistor ME4.

Note that the transistor ME4 can have the same structure as thetransistor ME3. Alternatively, the transistor ME4 may have a structuredifferent from that of the transistor ME3.

<<Conductive Film 520>>

The conductive film 520 includes a region overlapping with thesemiconductor film. In other words, the semiconductor film is providedbetween the conductive film 520 and the conductive film 504. This canimprove reliability of the transistor ME3 or the transistor ME4.

The conductive film 520 can be used for a second gate electrode of thetransistor ME4. The conductive film 520 can be regarded as part of thetransistor ME3 or the transistor ME4.

For example, a wiring through which the potential equal to that of theconductive film 504 can be supplied can be electrically connected to theconductive film 520.

For example, a material used for the wiring portion can be used for theconductive film 520. Specifically, conductive oxide, indium-containingconductive oxide, indium oxide, indium tin oxide, indium zinc oxide,indium zinc gallium oxide, zinc oxide, zinc oxide to which gallium isadded, or the like can be used for the conductive film 520.

<<Wiring Portion, Terminal Portion>>

The wiring portion includes a signal line, and the terminal portionincludes a connection electrode 519 (see FIG. 5).

The signal line is electrically connected to the connection electrode519. Part of the signal line can be used for the connection electrode519.

The connection electrode 519 is electrically connected to a flexibleprinted substrate FPC2 with the use of, for example, a conductive memberACF2.

The material that can be used for the signal line 711 or the connectionelectrode 719 can be used for the signal line or the connectionelectrode 519.

<<Conductive Member ACF2>>

The material that can be used for the conductive member ACF1 can be usedfor the conductive member ACF2.

<<Substrate 510>>

A material having heat resistance high enough to withstand heattreatment in the manufacturing process can be used for the substrate510.

For example, a layered material of a base 510A and an insulating film510B can be used for the substrate 510. The insulating film 510B has afunction of inhibiting diffusion of impurities contained in the base510A or impurities from the outside.

For example, a material that can be used for the substrate 710 can beused for the substrate 510. Alternatively, a light-blocking material canbe used for the substrate 510.

<<Insulating Film 570>>

For example, a single-layer material or a layered material in which aplurality of layers are stacked can be used for the insulating film 570.For example, a layered material including an insulating film thatprevents diffusion of impurities can be used for the insulating film570. Specifically, a layered material in which a resin and one or aplurality of films that are selected from a silicon oxide layer, asilicon nitride layer, a silicon oxynitride layer, and the like and thatprevent diffusion of impurities that pass through the resin and the likeare stacked can be used for the insulating film 570.

<<Bonding Layer 530>>

For the bonding layer 530, an inorganic material, an organic material, acomposite material of an inorganic material and an organic material, orthe like can be used.

For example, a material that can be used for the sealant 730 can be usedfor the bonding layer 530.

<<Bonding Layer 535>>

For the bonding layer 535, an inorganic material, an organic material, acomposite material of an inorganic material and an organic material, orthe like can be used.

For example, the material that can be used for the bonding layer 530 canbe used for the bonding layer 535.

<<Structure Example 2 of Display Panel>>

Another structure of the display panel of one embodiment of the presentinvention will be described with reference to FIGS. 1, 2, and 6 to 8.

FIG. 6 is a cross-sectional view illustrating structures of the displaypanel of one embodiment of the present invention taken along the cuttingplane lines X1-X2, X3-X4, and X5-X6 in FIG. 1.

FIG. 7A is a cross-sectional view illustrating structures of the firstdisplay portion 700F of the display panel of one embodiment of thepresent invention taken along the cutting plane lines X1-X2, X3-X4, andX5-X6 in FIG. 1. FIG. 7B is a cross-sectional view illustrating thestructure of a transistor.

FIG. 8 is a cross-sectional view illustrating structures of the seconddisplay portion 500F of the display panel of one embodiment of thepresent invention taken along the cutting plane lines X1-X2, X3-X4, andX5-X6 in FIG. 1.

Structures different from those in the display panel described abovewill be described in detail below, and the above description is referredto for the other similar structures.

<<First Display Portion 700F>>

The first display portion 700F is different from the first displayportion 700E described with reference to FIGS. 4A and 4B in that a flatfirst conductive film 751F and an optical film 770PF are provided, thestructure body KB1 is provided over the substrate 770, and top-gatetransistors MF1 and MF2 are provided.

For example, a polarizing plate containing a dichromatic pigment can beused for the optical film 770PF.

<<Second Display Portion 500F>>

The second display portion 500F is different from the second displayportion 500E described with reference to FIG. 3 in that the coloringfilm CF2 is not provided, a second display element 550FB that emits bluelight, green light, red light, or the like is provided, and the top-gatetransistors MF1 and MF2 are provided.

In one sub-pixel, the second display element 550FB that emits light of acolor different from that emitted from the second display elementprovided in another sub-pixel is used. For example, the second displayelement 550FB that emits blue light is used in one sub-pixel, and thesecond display element that emits green light or red light is used inanother sub-pixel.

Specifically, the second display element including a layer 553Fcontaining a luminescent material that emits blue light is used as thesecond display element 550FB. The second display element including alayer containing a luminescent material that emits green light or redlight is used in another sub-pixel.

Note that an evaporation method or an ink-jet method using a shadow maskcan be employed to form the layers containing luminescent materials. Inthat case, in one sub-pixel, the second display element 550FB that emitslight of a color different from that emitted from the second displayelement provided in another sub-pixel can be used.

Note that the second display element 550FB may have a concave shape, andemitted light may be gathered into the opening 751H (see FIG. 20). Thus,a region having a light-emitting function of the second display element550FB can be widened to a region not overlapping with the opening 751H.For example, the area of the region not overlapping with the opening751H can be more than 20% of the area of a region overlapping with theopening 751H. Accordingly, the density of current flowing through thesecond display element 550FB can be reduced, so that, for example, heatgeneration can be reduced, reliability can be improved, or the size ofthe opening 751H can be reduced.

<<Transistor MF1>>

The transistor MF1 includes the conductive film 704 having a regionoverlapping with the insulating film 710B and the semiconductor film 718having a region provided between the insulating film 710B and theconductive film 704. Note that the conductive film 704 functions as agate electrode (see FIG. 7B).

The semiconductor film 718 is includes a first region 718A, a secondregion 718B, and a third region 718C. The first region 718A and thesecond region 718B do not overlap with the conductive film 704. Thethird region 718C is positioned between the first region 718A and thesecond region 718B and overlaps with the conductive film 704.

The transistor MF1 includes the insulating film 706 between the thirdregion 718C and the conductive film 704. Note that the insulating film706 functions as a gate insulating film.

The first region 718A and the second region 718B have a lower resistancethan the third region 718C, and function as a source region and a drainregion.

Note that, for example, a method for controlling the resistivity of theoxide semiconductor film to be described later can be used as a methodfor forming the first region 718A and the second region 718B in thesemiconductor film 718. Specifically, plasma treatment using a gascontaining a rare gas can be used. For example, when the conductive film704 is used as a mask, the shape of part of the third region 718C can bethe same as the shape of an end portion of the conductive film 704 in aself-aligned manner.

The transistor MF1 includes the conductive film 712A in contact with thefirst region 718A and the conductive film 712B in contact with thesecond region 718B. The conductive film 712A and the conductive film712B function as a source electrode and a drain electrode.

A transistor that can be formed in the same process as the transistorMF1 can be used as the transistor MF2.

<Method for Controlling Resistivity of Oxide Semiconductor Film>

The method for controlling the resistivity of an oxide semiconductorfilm will be described.

An oxide semiconductor film with a certain resistivity can be used forthe conductive film 720, the first region 718A, or the second region718B.

For example, a method for controlling the concentration of impuritiessuch as hydrogen and water contained in the oxide semiconductor filmand/or the oxygen vacancies in the film can be used as the method forcontrolling the resistivity of an oxide semiconductor film.

Specifically, plasma treatment can be used as a method for increasing ordecreasing the concentration of impurities such as hydrogen and waterand/or the oxygen vacancies in the film.

Specifically, plasma treatment using a gas containing one or more kindsselected from a rare gas (He, Ne, Ar, Kr, Xe), hydrogen, boron,phosphorus, and nitrogen can be employed. For example, plasma treatmentin an Ar atmosphere, plasma treatment in a mixed gas atmosphere of Arand hydrogen, plasma treatment in an ammonia atmosphere, plasmatreatment in a mixed gas atmosphere of Ar and ammonia, or plasmatreatment in a nitrogen atmosphere can be employed. Thus, the oxidesemiconductor film can have a high carrier density and a lowresistivity.

Alternatively, hydrogen, boron, phosphorus, or nitrogen is added to theoxide semiconductor film by an ion implantation method, an ion dopingmethod, a plasma immersion ion implantation method, or the like, so thatthe oxide semiconductor film can have a low resistivity.

Alternatively, an insulating film containing hydrogen is formed incontact with the oxide semiconductor film, and the hydrogen is diffusedfrom the insulating film to the oxide semiconductor film, so that theoxide semiconductor film can have a high carrier density and a lowresistivity.

For example, an insulating film with a hydrogen concentration of greaterthan or equal to 1×10²² atoms/cm³ is formed in contact with the oxidesemiconductor film, in that case hydrogen can be effectively supplied tothe oxide semiconductor film. Specifically, a silicon nitride film canbe used as the insulating film formed in contact with the oxidesemiconductor film.

Hydrogen contained in the oxide semiconductor film reacts with oxygenbonded to a metal atom to be water, and an oxygen vacancy is formed in alattice from which oxygen is released (or a portion from which oxygen isreleased). Due to entry of hydrogen into the oxygen vacancy, an electronserving as a carrier is generated in some cases. Furthermore, bonding ofpart of hydrogen to oxygen bonded to a metal atom causes generation ofan electron serving as a carrier in some cases. Thus, the oxidesemiconductor film can have a high carrier density and a lowresistivity.

Specifically, an oxide semiconductor with a hydrogen concentrationmeasured by secondary ion mass spectrometry (SIMS) of greater than orequal to 8×10¹⁹ atoms/cm³, preferably greater than or equal to 1×10²⁰atoms/cm³, more preferably greater than or equal to 5×10²⁰ atoms/cm³ canbe suitably used for the conductive film 720.

On the other hand, an oxide semiconductor with a high resistivity can beused for a semiconductor film where a channel of a transistor is formed.

For example, an insulating film containing oxygen, in other words, aninsulating film capable of releasing oxygen, is formed in contact withan oxide semiconductor film, and the oxygen is supplied from theinsulating film to the oxide semiconductor film, so that oxygenvacancies in the film or at the interface can be filled. Thus, the oxidesemiconductor film can have a high resistivity.

For example, a silicon oxide film or a silicon oxynitride film can beused as the insulating film capable of releasing oxygen.

The oxide semiconductor film in which oxygen vacancies are filled andthe hydrogen concentration is reduced can be referred to as a highlypurified intrinsic or substantially highly purified intrinsic oxidesemiconductor film. The term “substantially intrinsic” refers to thestate in which an oxide semiconductor film has a carrier density lowerthan 8×10¹¹ /cm³, preferably lower than 1×10¹¹ /cm³, further preferablylower than 1×10¹⁰ /cm³. A highly purified intrinsic or substantiallyhighly purified intrinsic oxide semiconductor film has few carriergeneration sources and thus can have a low carrier density. The highlypurified intrinsic or substantially highly purified intrinsic oxidesemiconductor film has a low density of defect states and accordinglycan have a low density of trap states.

Furthermore, a transistor including the highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor film has anextremely low off-state current; even when an element has a channelwidth of 1×10⁶ μm and a channel length of 10 μm, the off-state currentcan be lower than or equal to the measurement limit of a semiconductorparameter analyzer, that is, lower than or equal to 1×10⁻¹³ A, at avoltage (drain voltage) between a source electrode and a drain electrodeof from 1 V to 10 V.

The transistor in which a channel region is formed in the oxidesemiconductor film that is a highly purified intrinsic or substantiallyhighly purified intrinsic oxide semiconductor film can have a smallchange in electrical characteristics and high reliability.

Specifically, an oxide semiconductor has a hydrogen concentration whichis measured by secondary ion mass spectrometry (SIMS) of lower than orequal to 2×10²⁰ atoms/cm³, preferably lower than or equal to 5×10¹⁹atoms/cm³, more preferably lower than or equal to 1×10¹⁹ atoms/cm³, morepreferably lower than 5×10¹⁸ atoms/cm³, more preferably lower than orequal to 1×10¹⁸ atoms/cm³, more preferably lower than or equal to 5×10¹⁷atoms/cm³, more preferably lower than or equal to 1×10¹⁶ atoms/cm³ canbe favorably used for a semiconductor film where a channel of atransistor is formed.

An oxide semiconductor film that has a higher hydrogen concentrationand/or a larger number of oxygen vacancies and that has a lowerresistivity than the semiconductor film 718 is used as the conductivefilm 720.

The hydrogen concentration in the conductive film 720 is twice or more,preferably ten times or more that in the semiconductor film 718.

The resistivity of the conductive film 720 is greater than or equal to1×10⁻⁸ times and less than 1×10⁻¹ times that of the semiconductor film718.

Specifically, the resistivity of the conductive film 720 is higher thanor equal to 1×10⁻³ Ωcm and lower than 1×10⁴ Ωcm, preferably higher thanor equal to 1×10⁻³ Ωcm and lower than 1×10⁻¹ Ωcm.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 2

In this embodiment, a structure of a transistor that can be used in thedisplay panel of one embodiment of the present invention will bedescribed with reference to FIGS. 9A to 9D.

<Structure Example of Semiconductor Device>

FIG. 9A is a top view of a transistor 100. FIG. 9C is a cross-sectionalview taken along the cutting plane line X1-X2 in FIG. 9A, and FIG. 9D isa cross-sectional view taken along the cutting plane line Y1-Y2 in FIG.9A. Note that in FIG. 9A, some components of the transistor 100 (e.g.,an insulating film serving as a gate insulating film) are notillustrated to avoid complexity. Furthermore, the direction of thecutting plane line X1-X2 may be called a channel length direction, andthe direction of the cutting plane line Y1-Y2 may be called a channelwidth direction. As in FIG. 9A, some components are not illustrated insome cases in top views of transistors described below.

The transistor 100 can be used in the display panel described inEmbodiment 1.

For example, when the transistor 100 is used as the transistor ME1, asubstrate 102, a conductive film 104, a stacked film of an insulatingfilm 106 and an insulating film 107, an oxide semiconductor film 108, aconductive film 112 a, a conductive film 112 b, a stacked film of aninsulating film 114 and an insulating film 116, and an insulating film118 can be referred to as the substrate 710, the conductive film 704,the insulating film 706, the semiconductor film 718, the conductive film712A, the conductive film 712B, the insulating film 721A, and theinsulating film 721B, respectively.

The transistor 100 includes the conductive film 104 functioning as agate electrode over the substrate 102, the insulating film 106 over thesubstrate 102 and the conductive film 104, the insulating film 107 overthe insulating film 106, the oxide semiconductor film 108 over theinsulating film 107, and the conductive films 112 a and 112 bfunctioning as source and drain electrodes electrically connected to theoxide semiconductor film 108. Over the transistor 100, specifically,over the conductive films 112 a and 112 b and the oxide semiconductorfilm 108, the insulating films 114, 116, and 118 are provided. Theinsulating films 114, 116, and 118 function as protective insulatingfilms for the transistor 100.

The oxide semiconductor film 108 includes an oxide semiconductor film108 a on the conductive film 104 side and an oxide semiconductor film108 b over the oxide semiconductor film 108 a. The conductive film 104serves as a gate electrode. The insulating films 106 and 107 function asgate insulating films of the transistor 100.

In-M oxide (M is Ti, Ga, Sn, Y, Zr, La, Ce, Nd, or Hf) or In-M-Zn oxidecan be used for the oxide semiconductor film 108. It is particularlypreferable to use In-M-Zn oxide for the oxide semiconductor film 108.

The oxide semiconductor film 108 a includes a first region in which theatomic proportion of In is larger than the atomic proportion of M. Theoxide semiconductor film 108 b includes a second region in which theatomic proportion of In is smaller than that in the oxide semiconductorfilm 108 a. The second region includes a portion thinner than the firstregion.

The oxide semiconductor film 108 a including the first region in whichthe atomic proportion of In is larger than that of M can increase thefield-effect mobility (also simply referred to as mobility or μFE) ofthe transistor 100. Specifically, the field-effect mobility of thetransistor 100 can exceed 10 cm²/Vs.

For example, the use of the transistor with high field-effect mobilityfor a gate driver that generates a gate signal (specifically, ademultiplexer connected to an output terminal of a shift registerincluded in a gate driver) allows a semiconductor device or a displaydevice to have a narrow frame.

On the other hand, the oxide semiconductor film 108 a including thefirst region in which the atomic proportion of In is larger than that ofM makes it easier to change electrical characteristics of the transistor100 in light irradiation. However, in the semiconductor device of oneembodiment of the present invention, the oxide semiconductor film 108 bis formed over the oxide semiconductor film 108 a. In addition, thethickness of the channel region in the oxide semiconductor film 108 b issmaller than the thickness of the oxide semiconductor film 108 a.

Furthermore, the oxide semiconductor film 108 b includes the secondregion in which the atomic proportion of In is smaller than the oxidesemiconductor film 108 a and thus has larger Eg than that of the oxidesemiconductor film 108 a. For this reason, the oxide semiconductor film108 which is a layered structure of the oxide semiconductor film 108 aand the oxide semiconductor film 108 b has high resistance to a negativebias stress test with light irradiation.

The amount of light absorbed by the oxide semiconductor film 108 can bereduced during light irradiation. As a result, the change in electricalcharacteristics of the transistor 100 due to light irradiation can bereduced. In the semiconductor device of one embodiment of the presentinvention, the insulating film 114 or the insulating film 116 includesexcess oxygen. This structure can further reduce the change inelectrical characteristics of the transistor 100 due to lightirradiation.

Here, the oxide semiconductor film 108 is described in detail withreference to FIG. 9B.

FIG. 9B is a cross-sectional enlarged view of the oxide semiconductorfilm 108 and the vicinity thereof in the transistor 100 illustrated inFIG. 9C.

In FIG. 9B, t1, t2-1, and t2-2 denote a thickness of the oxidesemiconductor film 108 a, one thickness of the oxide semiconductor film108 b, and the other thickness the oxide semiconductor film 108 b,respectively. The oxide semiconductor film 108 b over the oxidesemiconductor film 108 a prevents the oxide semiconductor film 108 afrom being exposed to an etching gas, an etchant, or the like when theconductive films 112 a and 112 b are formed. This is why the oxidesemiconductor film 108 a is not or is hardly reduced in thickness. Incontrast, in the oxide semiconductor film 108 b, a portion notoverlapping with the conductive films 112 a and 112 b is etched byformation of the conductive films 112 a and 112 b, so that a depressionis formed in the etched region. In other words, a thickness of the oxidesemiconductor film 108 b in a region overlapping with the conductivefilms 112 a and 112 b is t2-1, and a thickness of the oxidesemiconductor film 108 b in a region not overlapping with the conductivefilms 112 a and 112 b is t2-2.

As for the relationships between the thicknesses of the oxidesemiconductor film 108 a and the oxide semiconductor film 108 b,t2-1>t1>t2-2 is preferable. A transistor with the thicknessrelationships can have high field-effect mobility and less variation inthreshold voltage in light irradiation.

When oxygen vacancy is formed in the oxide semiconductor film 108included in the transistor 100, electrons serving as carriers aregenerated; as a result, the transistor 100 tends to be normally-on.Therefore, for stable transistor characteristics, it is important toreduce oxygen vacancy in the oxide semiconductor film 108 particularlyoxygen vacancy in the oxide semiconductor film 108 a. In the structureof the transistor of one embodiment of the present invention, excessoxygen is introduced into an insulating film over the oxidesemiconductor film 108, here, the insulating film 114 and/or theinsulating film 116 over the oxide semiconductor film 108, wherebyoxygen is moved from the insulating film 114 and/or the insulating film116 to the oxide semiconductor film 108 to fill oxygen vacancy in theoxide semiconductor film 108 particularly in the oxide semiconductorfilm 108 a.

It is preferable that the insulating films 114 and 116 each include aregion (oxygen excess region) including oxygen in excess of that in thestoichiometric composition. In other words, the insulating films 114 and116 are insulating films capable of releasing oxygen. Note that theoxygen excess region is formed in the insulating films 114 and 116 insuch a manner that oxygen is introduced into the insulating films 114and 116 after the deposition, for example. As a method for introducingoxygen, an ion implantation method, an ion doping method, a plasmaimmersion ion implantation method, plasma treatment, or the like may beemployed.

In order to fill oxygen vacancy in the oxide semiconductor film 108 a,the thickness of the portion including the channel region and thevicinity of the channel region in the oxide semiconductor film 108 b ispreferably small, and t2-2<t1 is preferably satisfied. For example, thethickness of the portion including the channel region and the vicinityof the channel region in the oxide semiconductor film 108 b ispreferably more than or equal to 1 nm and less than or equal to 20 nm,more preferably more than or equal to 3 nm and less than or equal to 10nm.

Other constituent elements of the semiconductor device of thisembodiment are described below in detail.

<<Substrate>>

There is no particular limitation on the property of a material and thelike of the substrate 102 as long as the material has heat resistanceenough to withstand at least heat treatment to be performed later. Forexample, a glass substrate, a ceramic substrate, a quartz substrate, ora sapphire substrate may be used as the substrate 102. Alternatively, asingle crystal semiconductor substrate or a polycrystallinesemiconductor substrate of silicon or silicon carbide, a compoundsemiconductor substrate of silicon germanium, an SOI substrate, or thelike can be used as the substrate 102.

Alternatively, any of these substrates provided with a semiconductorelement may be used as the substrate 102.

In the case where a glass substrate is used as the substrate 102, alarge substrate having any of the following sizes can be used: the 6thgeneration (1500 mm×1850 mm), the 7th generation (1870 mm×2200 mm), the8th generation (2200 mm×2400 mm), the 9th generation (2400 mm×2800 mm),and the 10th generation (2950 mm×3400 mm). Thus, a large display devicecan be manufactured.

Alternatively, a flexible substrate may be used as the substrate 102,and the transistor 100 may be provided directly on the flexiblesubstrate. Alternatively, a separation layer may be provided between thesubstrate 102 and the transistor 100. The separation layer can be usedwhen part or the whole of a semiconductor device formed over theseparation layer is separated from the substrate 102 and transferredonto another substrate. In such a case, the transistor 100 can betransferred to a substrate having low heat resistance or a flexiblesubstrate as well.

<<Conductive Film Functioning as Gate Electrode and Source and DrainElectrodes>>

The conductive film 104 functioning as a gate electrode and theconductive films 112 a and 112 b functioning as a source electrode and adrain electrode, respectively, can each be formed using a metal elementselected from chromium (Cr), copper (Cu), aluminum (Al), gold (Au),silver (Ag), zinc (Zn), molybdenum (Mo), tantalum (Ta), titanium (Ti),tungsten (W), manganese (Mn), nickel (Ni), iron (Fe), and cobalt (Co);an alloy including any of these metal element as its component; an alloyincluding a combination of any of these metal elements; or the like.

Furthermore, the conductive films 104, 112 a, and 112 b may have asingle-layer structure or a stacked-layer structure of two or morelayers. For example, a single-layer structure of an aluminum filmincluding silicon, a two-layer structure in which a titanium film isstacked over an aluminum film, a two-layer structure in which a titaniumfilm is stacked over a titanium nitride film, a two-layer structure inwhich a tungsten film is stacked over a titanium nitride film, atwo-layer structure in which a tungsten film is stacked over a tantalumnitride film or a tungsten nitride film, and a three-layer structure inwhich a titanium film, an aluminum film, and a titanium film are stackedin this order can be given. Alternatively, an alloy film or a nitridefilm in which aluminum and one or more elements selected from titanium,tantalum, tungsten, molybdenum, chromium, neodymium, and scandium arecombined may be used.

The conductive films 104, 112 a, and 112 b can be formed using alight-transmitting conductive material such as indium tin oxide, indiumoxide including tungsten oxide, indium zinc oxide including tungstenoxide, indium oxide including titanium oxide, indium tin oxide includingtitanium oxide, indium zinc oxide, or indium tin oxide to which siliconoxide is added.

A Cu—X alloy film (X is Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti) may be usedfor the conductive films 104, 112 a, and 112 b. Use of a Cu—X alloy filmenables the manufacturing cost to be reduced because wet etching processcan be used in the processing.

<<Insulating Film Functioning as Gate Insulating Film>>

As each of the insulating films 106 and 107 functioning as gateinsulating films of the transistor 100, an insulating film including atleast one of the following films formed by a plasma enhanced chemicalvapor deposition (PECVD) method, a sputtering method, or the like can beused: a silicon oxide film, a silicon oxynitride film, a silicon nitrideoxide film, a silicon nitride film, an aluminum oxide film, a hafniumoxide film, an yttrium oxide film, a zirconium oxide film, a galliumoxide film, a tantalum oxide film, a magnesium oxide film, a lanthanumoxide film, a cerium oxide film, and a neodymium oxide film. Note thatinstead of a stacked-layer structure of the insulating films 106 and107, an insulating film of a single layer formed using a materialselected from the above or an insulating film of three or more layersmay be used.

The insulating film 106 has a function as a blocking film which inhibitspenetration of oxygen. For example, in the case where excess oxygen issupplied to the insulating film 107, the insulating film 114, theinsulating film 116, and/or the oxide semiconductor film 108, theinsulating film 106 can inhibit penetration of oxygen.

Note that the insulating film 107 that is in contact with the oxidesemiconductor film 108 functioning as a channel region of the transistor100 is preferably an oxide insulating film and preferably includes aregion including oxygen in excess of the stoichiometric composition(oxygen-excess region). In other words, the insulating film 107 is aninsulating film capable of releasing oxygen. In order to provide theoxygen excess region in the insulating film 107, the insulating film 107is formed in an oxygen atmosphere, for example. Alternatively, theoxygen excess region may be formed by introduction of oxygen into theinsulating film 107 after the deposition. As a method for introducingoxygen, an ion implantation method, an ion doping method, a plasmaimmersion ion implantation method, plasma treatment, or the like may beemployed.

In the case where hafnium oxide is used for the insulating film 107, thefollowing effect is attained. Hafnium oxide has a higher dielectricconstant than silicon oxide and silicon oxynitride. Therefore, by usinghafnium oxide, the thickness of the insulating film 107 can be madelarge as compared with the case where silicon oxide is used; thus,leakage current due to tunnel current can be low. That is, it ispossible to provide a transistor with a low off-state current. Moreover,hafnium oxide with a crystalline structure has higher dielectricconstant than hafnium oxide with an amorphous structure. Therefore, itis preferable to use hafnium oxide with a crystalline structure in orderto provide a transistor with a low off-state current. Examples of thecrystalline structure include a monoclinic crystal structure and a cubiccrystal structure. Note that one embodiment of the present invention isnot limited thereto.

In this embodiment, a silicon nitride film is formed as the insulatingfilm 106, and a silicon oxide film is formed as the insulating film 107.The silicon nitride film has a higher dielectric constant than a siliconoxide film and needs a larger thickness for capacitance equivalent tothat of the silicon oxide film. Thus, when the silicon nitride film isincluded in the gate insulating film of the transistor 100, the physicalthickness of the insulating film can be increased. This makes itpossible to reduce a decrease in withstand voltage of the transistor 100and furthermore to increase the withstand voltage, thereby reducingelectrostatic discharge damage to the transistor 100.

<<Oxide Semiconductor Film>>

The oxide semiconductor film 108 can be formed using the materialsdescribed above.

In the case where the oxide semiconductor film 108 includes In-M-Znoxide, it is preferable that the atomic ratio of metal elements of asputtering target used for forming the In-M-Zn oxide satisfy In M and ZnM As the atomic ratio of metal elements of such a sputtering target,In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, In:M:Zn=2:1:3, In:M:Zn=3:1:2, andIn:M:Zn=4:2:4.1 are preferable.

In the case where the oxide semiconductor film 108 is formed of In-M-Znoxide, it is preferable to use a target including polycrystallineIn-M-Zn oxide as the sputtering target. The use of the target includingpolycrystalline In-M-Zn oxide facilitates formation of the oxidesemiconductor film 108 having crystallinity. Note that the atomic ratiosof metal elements in the formed oxide semiconductor film 108 vary fromthe above atomic ratio of metal elements of the sputtering target withina range of ±40% as an error. For example, when a sputtering target withan atomic ratio of In to Ga and Zn of 4:2:4.1 is used, the atomic ratioof In to Ga and Zn in the oxide semiconductor film 108 may be 4:2:3 orin the vicinity of 4:2:3.

The oxide semiconductor film 108 a can be formed using the sputteringtarget having an atomic ratio of In:M:Zn=2:1:3, In:M:Zn=3:1:2, orIn:M:Zn=4:2:4.1. The oxide semiconductor film 108 b can be formed usingthe sputtering target having an atomic ratio of In:M:Zn=1:1:1 orIn:M:Zn=1:1:1.2. Note that the atomic ratio of metal elements in asputtering target used for forming the oxide semiconductor film 108 bdoes not necessarily satisfy In M and Zn and may satisfy In and Zn<M,such as In:M:Zn=3:2:1.

The energy gap of the oxide semiconductor film 108 is 2 eV or more,preferably 2.5 eV or more, further preferably 3 eV or more. The use ofan oxide semiconductor having a wide energy gap can reduce off-statecurrent of the transistor 100. In particular, an oxide semiconductorfilm having an energy gap more than or equal to 2 eV, preferably morethan or equal to 2 eV and less than or equal to 3.0 eV is preferablyused as the oxide semiconductor film 108 a, and an oxide semiconductorfilm having an energy gap more than or equal to 2.5 eV and less than orequal to 3.5 eV is preferably used as the oxide semiconductor film 108b. Furthermore, the oxide semiconductor film 108 b preferably has ahigher energy gap than that of the oxide semiconductor film 108 a.

Each thickness of the oxide semiconductor film 108 a and the oxidesemiconductor film 108 b is more than or equal to 3 nm and less than orequal to 200 nm, preferably more than or equal to 3 nm and less than orequal to 100 nm, more preferably more than or equal to 3 nm and lessthan or equal to 50 nm. Note that the above-described thicknessrelationships between them are preferably satisfied.

An oxide semiconductor film with low carrier density is used as theoxide semiconductor film 108 b. For example, the carrier density of theoxide semiconductor film 108 b is lower than or equal to 1×10¹⁷ /cm³,preferably lower than or equal to 1×10¹⁵ /cm³, further preferably lowerthan or equal to 1×10¹³ /cm³, still further preferably lower than orequal to 1×10¹¹ /cm³.

Note that, without limitation to the compositions and materialsdescribed above, a material with an appropriate composition may be useddepending on required semiconductor characteristics and electricalcharacteristics (e.g., field-effect mobility and threshold voltage) of atransistor. Furthermore, in order to obtain required semiconductorcharacteristics of a transistor, it is preferable that the carrierdensity, the impurity concentration, the defect density, the atomicratio of a metal element to oxygen, the interatomic distance, thedensity, and the like of the oxide semiconductor film 108 a and theoxide semiconductor film 108 b be set to be appropriate.

Note that it is preferable to use, as the oxide semiconductor film 108 aand the oxide semiconductor film 108 b, an oxide semiconductor film inwhich the impurity concentration is low and the density of defect statesis low, in which case the transistor can have more excellent electricalcharacteristics. Here, the state in which the impurity concentration islow and the density of defect states is low (the amount of oxygenvacancy is small) is referred to as “highly purified intrinsic” or“substantially highly purified intrinsic”. A highly purified intrinsicor substantially highly purified intrinsic oxide semiconductor film hasfew carrier generation sources, and thus can have a low carrier density.Thus, a transistor in which a channel region is formed in the oxidesemiconductor film rarely has a negative threshold voltage (is rarelynormally on). A highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor film has a low density of defectstates and accordingly has few carrier traps in some cases. Furthermore,the highly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film has an extremely low off-state current; evenwhen an element has a channel width of 1×10⁶ μm and a channel length of10 μm, the off-state current can be less than or equal to themeasurement limit of a semiconductor parameter analyzer, that is, lessthan or equal to 1×10⁻¹³ A, at a voltage (drain voltage) between asource electrode and a drain electrode of from 1 V to 10 V.

Accordingly, the transistor in which the channel region is formed in thehighly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film can have a small change in electricalcharacteristics and high reliability. Charges trapped by the trap statesin the oxide semiconductor film take a long time to be released and maybehave like fixed charges. Thus, the transistor whose channel region isformed in the oxide semiconductor film having a high density of trapstates has unstable electrical characteristics in some cases. Asexamples of the impurities, hydrogen, nitrogen, alkali metal, alkalineearth metal, and the like are given.

Hydrogen included in the oxide semiconductor film reacts with oxygenbonded to a metal atom to be water, and also causes oxygen vacancy in alattice from which oxygen is released (or a portion from which oxygen isreleased). Due to entry of hydrogen into the oxygen vacancy, an electronserving as a carrier is generated in some cases. Furthermore, in somecases, bonding of part of hydrogen to oxygen bonded to a metal atomcauses generation of an electron serving as a carrier. Thus, atransistor including an oxide semiconductor film which contains hydrogenis likely to be normally on. Accordingly, it is preferable that hydrogenbe reduced as much as possible in the oxide semiconductor film 108.Specifically, in the oxide semiconductor film 108, the concentration ofhydrogen which is measured by SIMS is lower than or equal to 2×10²⁰atoms/cm³, preferably lower than or equal to 5×10¹⁹ atoms/cm³, furtherpreferably lower than or equal to 1×10¹⁹ atoms/cm³, further preferablylower than or equal to 5×10¹⁸ atoms/cm³, further preferably lower thanor equal to 1×10¹⁸ atoms/cm³, further preferably lower than or equal to5×10¹⁷ atoms/cm³, and further preferably lower than or equal to 1×10¹⁶atoms/cm³.

When silicon or carbon that is one of elements belonging to Group 14 isincluded in the oxide semiconductor film 108 a, oxygen vacancy isincreased in the oxide semiconductor film 108 a, and the oxidesemiconductor film 108 a becomes an n-type film. Thus, the concentrationof silicon or carbon (the concentration is measured by SIMS) in theoxide semiconductor film 108 a or the concentration of silicon or carbon(the concentration is measured by SIMS) in the vicinity of an interfacewith the oxide semiconductor film 108 a is set to be lower than or equalto 2×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁷ atoms/cm³.

In addition, the concentration of alkali metal or alkaline earth metalof the oxide semiconductor film 108 a, which is measured by SIMS, islower than or equal to 1×10¹⁸ atoms/cm³, preferably lower than or equalto 2×10¹⁶ atoms/cm³. Alkali metal and alkaline earth metal mightgenerate carriers when bonded to an oxide semiconductor, in which casethe off-state current of the transistor might be increased. Therefore,it is preferable to reduce the concentration of alkali metal or alkalineearth metal of the oxide semiconductor film 108 a.

Furthermore, when including nitrogen, the oxide semiconductor film 108 aeasily becomes n-type by generation of electrons serving as carriers andan increase of carrier density. Thus, a transistor including an oxidesemiconductor film which contains nitrogen is likely to have normally-oncharacteristics. For this reason, nitrogen in the oxide semiconductorfilm is preferably reduced as much as possible; the concentration ofnitrogen which is measured by SIMS is preferably set to be, for example,lower than or equal to 5×10¹⁸ atoms/cm³.

Each of the oxide semiconductor films 108 a and 108 b may have anon-single-crystal structure, for example. The non-single crystalstructure includes a c-axis aligned crystalline oxide semiconductor(CAAC-OS), a polycrystalline structure, a microcrystalline structure, oran amorphous structure, for example. Among the non-single crystalstructure, the amorphous structure has the highest density of defectstates, whereas CAAC-OS has the lowest density of defect states.

<<Insulating Film Functioning as Protective Insulating Film ofTransistor>>

The insulating films 114 and 116 each have a function of supplyingoxygen to the oxide semiconductor film 108. The insulating film 118 hasa function of a protective insulating film of the transistor 100. Theinsulating films 114 and 116 include oxygen. Furthermore, the insulatingfilm 114 is an insulating film which can transmit oxygen. The insulatingfilm 114 also functions as a film which relieves damage to the oxidesemiconductor film 108 at the time of forming the insulating film 116 ina later step.

A silicon oxide film, a silicon oxynitride film, or the like with athickness greater than or equal to 5 nm and less than or equal to 150nm, preferably greater than or equal to 5 nm and less than or equal to50 nm can be used as the insulating film 114.

In addition, it is preferable that the number of defects in theinsulating film 114 be small and typically, the spin densitycorresponding to a signal that appears at g=2.001 due to a dangling bondof silicon be lower than or equal to 3×10¹⁷ spins/cm³ by electron spinresonance (ESR) measurement. This is because if the density of defectsin the insulating film 114 is high, oxygen is bonded to the defects andthe amount of oxygen that transmits the insulating film 114 isdecreased.

Note that all oxygen entering the insulating film 114 from the outsidedoes not move to the outside of the insulating film 114 and some oxygenremains in the insulating film 114. Furthermore, movement of oxygenoccurs in the insulating film 114 in some cases in such a manner thatoxygen enters the insulating film 114 and oxygen included in theinsulating film 114 moves to the outside of the insulating film 114.When an oxide insulating film which can transmit oxygen is formed as theinsulating film 114, oxygen released from the insulating film 116provided over the insulating film 114 can be moved to the oxidesemiconductor film 108 through the insulating film 114.

Note that the insulating film 114 can be formed using an oxideinsulating film having a low density of states due to nitrogen oxide.Note that the density of states due to nitrogen oxide can be formedbetween the energy of the valence band maximum (E_(v_os)) and the energyof the conduction band minimum (E_(c_os)) of the oxide semiconductorfilm. A silicon oxynitride film that releases less nitrogen oxide, analuminum oxynitride film that releases less nitrogen oxide, and the likecan be used as the above oxide insulating film.

Note that a silicon oxynitride film that releases less nitrogen oxide isa film of which the amount of released ammonia is larger than the amountof released nitrogen oxide in TDS analysis; the amount of releasedammonia is typically greater than or equal to 1×10¹⁸ /cm³ and less thanor equal to 5×10¹⁹ /cm³. Note that the amount of released ammonia is theamount of ammonia released by heat treatment with which the surfacetemperature of a film becomes higher than or equal to 50° C. and lowerthan or equal to 650° C., preferably higher than or equal to 50° C. andlower than or equal to 550° C.

Nitrogen oxide (NO_(x); x is greater than 0 and less than or equal to 2,preferably greater than or equal to 1 and less than or equal to 2),typically NO₂ or NO, forms levels in the insulating film 114, forexample. The level is positioned in the energy gap of the oxidesemiconductor film 108. Therefore, when nitrogen oxide is diffused tothe interface between the insulating film 114 and the oxidesemiconductor film 108, an electron is in some cases trapped by thelevel on the insulating film 114 side. As a result, the trapped electronremains in the vicinity of the interface between the insulating film 114and the oxide semiconductor film 108; thus, the threshold voltage of thetransistor is shifted in the positive direction.

Nitrogen oxide reacts with ammonia and oxygen in heat treatment. Sincenitrogen oxide included in the insulating film 114 reacts with ammoniaincluded in the insulating film 116 in heat treatment, nitrogen oxideincluded in the insulating film 114 is reduced. Therefore, an electronis hardly trapped at the vicinity of the interface between theinsulating film 114 and the oxide semiconductor film 108.

By using such an oxide insulating film, the insulating film 114 canreduce the shift in the threshold voltage of the transistor, which leadsto a smaller change in the electrical characteristics of the transistor.

Note that in an ESR spectrum at 100K or lower of the insulating film114, by heat treatment of a manufacturing process of the transistor,typically heat treatment at a temperature higher than or equal to 300°C. and lower than 350° C., a first signal that appears at a g-factor ofgreater than or equal to 2.037 and less than or equal to 2.039, a secondsignal that appears at a g-factor of greater than or equal to 2.001 andless than or equal to 2.003, and a third signal that appears at ag-factor of greater than or equal to 1.964 and less than or equal to1.966 are observed. The split width of the first and second signals andthe split width of the second and third signals that are obtained by ESRmeasurement using an X-band are each approximately 5 mT. The sum of thespin densities of the first signal that appears at a g-factor of greaterthan or equal to 2.037 and less than or equal to 2.039, the secondsignal that appears at a g-factor of greater than or equal to 2.001 andless than or equal to 2.003, and the third signal that appears at ag-factor of greater than or equal to 1.964 and less than or equal to1.966 is lower than 1×10¹⁸ spins/cm³, typically higher than or equal to1×10¹⁷ spins/cm³ and lower than 1×10¹⁸ spins/cm³.

In the ESR spectrum at 100K or lower, the first signal that appears at ag-factor of greater than or equal to 2.037 and less than or equal to2.039, the second signal that appears at a g-factor of greater than orequal to 2.001 and less than or equal to 2.003, and the third signalthat appears at a g-factor of greater than or equal to 1.964 and lessthan or equal to 1.966 correspond to signals attributed to nitrogenoxide (NO_(x); x is greater than 0 and less than or equal to 2,preferably greater than or equal to 1 and less than or equal to 2).Typical examples of nitrogen oxide include nitrogen monoxide andnitrogen dioxide. In other words, the lower the total spin density ofthe first signal that appears at a g-factor of greater than or equal to2.037 and less than or equal to 2.039, the second signal that appears ata g-factor of greater than or equal to 2.001 and less than or equal to2.003, and the third signal that appears at a g-factor of greater thanor equal to 1.964 and less than or equal to 1.966 is, the lower thecontent of nitrogen oxide in the oxide insulating film is.

The concentration of nitrogen of the above oxide insulating filmmeasured by SIMS is lower than or equal to 6×10²⁰ atoms/cm³.

The above oxide insulating film is formed by a PECVD method at a filmsurface temperature higher than or equal to 220° C. and lower than orequal to 350° C. using silane and dinitrogen monoxide, whereby a denseand hard film can be formed.

The insulating film 116 is formed using an oxide insulating film thatcontains oxygen in excess of that in the stoichiometric composition.Part of oxygen is released by heating from the oxide insulating filmincluding oxygen in excess of that in the stoichiometric composition.The oxide insulating film including oxygen in excess of that in thestoichiometric composition is an oxide insulating film of which theamount of released oxygen converted into oxygen atoms is greater than orequal to 1.0×10¹⁹ atoms/cm³, preferably greater than or equal to3.0×10²⁰ atoms/cm³ in TDS analysis. Note that the temperature of thefilm surface in the TDS analysis is preferably higher than or equal to100° C. and lower than or equal to 700° C., or higher than or equal to100° C. and lower than or equal to 500° C.

A silicon oxide film, a silicon oxynitride film, or the like with athickness greater than or equal to 30 nm and less than or equal to 500nm, preferably greater than or equal to 50 nm and less than or equal to400 nm can be used as the insulating film 116.

It is preferable that the number of defects in the insulating film 116be small, and typically the spin density corresponding to a signal whichappears at g=2.001 due to a dangling bond of silicon be lower than1.5×10¹⁸ spins/cm³, preferably lower than or equal to 1×10¹⁸ spins/cm³by ESR measurement. Note that the insulating film 116 is provided moreapart from the oxide semiconductor film 108 than the insulating film 114is; thus, the insulating film 116 may have higher density of defectsthan the insulating film 114.

Furthermore, the insulating films 114 and 116 can be formed usinginsulating films formed of the same kinds of materials; thus, a boundarybetween the insulating films 114 and 116 cannot be clearly observed insome cases. Thus, in this embodiment, the boundary between theinsulating films 114 and 116 is shown by a dashed line. Although atwo-layer structure of the insulating films 114 and 116 is described inthis embodiment, the present invention is not limited to this. Forexample, a single-layer structure of the insulating film 114 may beemployed.

The insulating film 118 includes nitrogen. Alternatively, the insulatingfilm 118 includes nitrogen and silicon. The insulating film 118 has afunction of blocking oxygen, hydrogen, water, alkali metal, alkalineearth metal, or the like. It is possible to prevent outward diffusion ofoxygen from the oxide semiconductor film 108, outward diffusion ofoxygen included in the insulating films 114 and 116, and entry ofhydrogen, water, or the like into the oxide semiconductor film 108 fromthe outside by providing the insulating film 118. A nitride insulatingfilm, for example, can be used as the insulating film 118. The nitrideinsulating film is formed using silicon nitride, silicon nitride oxide,aluminum nitride, aluminum nitride oxide, or the like. Note that insteadof the nitride insulating film having a blocking effect against oxygen,hydrogen, water, alkali metal, alkaline earth metal, and the like, anoxide insulating film having a blocking effect against oxygen, hydrogen,water, and the like may be provided. As the oxide insulating film havinga blocking effect against oxygen, hydrogen, water, and the like, analuminum oxide film, an aluminum oxynitride film, a gallium oxide film,a gallium oxynitride film, an yttrium oxide film, an yttrium oxynitridefilm, a hafnium oxide film, a hafnium oxynitride film, and the like canbe given.

Although the variety of films such as the conductive films, theinsulating films, and the oxide semiconductor films which are describedabove can be formed by a sputtering method or a PECVD method, such filmsmay be formed by another method, e.g., a thermal CVD method.

Examples of the thermal CVD method include a metal organic chemicalvapor deposition (MOCVD) method and an atomic layer deposition (ALD)method.

A thermal CVD method has an advantage that no defect due to plasmadamage is generated since it does not utilize plasma for forming a film.

Deposition by a thermal CVD method may be performed in such a mannerthat a source gas and an oxidizer are supplied to the chamber at a timeso that the pressure in a chamber is set to an atmospheric pressure or areduced pressure, and react with each other in the vicinity of thesubstrate or over the substrate.

Deposition by an ALD method may be performed in such a manner that thepressure in a chamber is set to an atmospheric pressure or a reducedpressure, source gases for reaction are sequentially introduced into thechamber, and then the sequence of the gas introduction is repeated. Forexample, two or more kinds of source gases are sequentially supplied tothe chamber by switching respective switching valves (also referred toas high-speed valves). For example, a first source gas is introduced, aninert gas (e.g., argon or nitrogen) or the like is introduced at thesame time as or after the introduction of the first source gas so thatthe source gases are not mixed, and then a second source gas isintroduced. Note that in the case where the first source gas and theinert gas are introduced at a time, the inert gas serves as a carriergas, and the inert gas may also be introduced at the same time as theintroduction of the second source gas. Alternatively, the first sourcegas may be exhausted by vacuum evacuation instead of the introduction ofthe inert gas, and then the second source gas may be introduced. Thefirst source gas is adsorbed on the surface of the substrate to form afirst layer; then the second source gas is introduced to react with thefirst layer; as a result, a second layer is stacked over the firstlayer, so that a thin film is formed. The sequence of the gasintroduction is repeated plural times until a desired thickness isobtained, whereby a thin film with excellent step coverage can beformed. The thickness of the thin film can be adjusted by the number ofrepetition times of the sequence of the gas introduction; therefore, anALD method makes it possible to accurately adjust a thickness and thusis suitable for manufacturing a minute FET.

The variety of films such as the conductive films, the insulating films,the oxide semiconductor films, and the metal oxide films in thisembodiment can be formed by a thermal CVD method such as an MOCVD methodor an ALD method. For example, in the case where an In—Ga—Zn—O film isformed, trimethylindium, trimethylgallium, and dimethylzinc are used.Note that the chemical formula of trimethylindium is In(CH₃)₃. Thechemical formula of trimethylgallium is Ga(CH₃)₃. The chemical formulaof dimethylzinc is Zn(CH₃)₂. Without limitation to the abovecombination, triethylgallium (chemical formula: Ga(C₂H₅)₃) can be usedinstead of trimethylgallium and diethylzinc (chemical formula:Zn(C₂H₅)₂) can be used instead of dimethylzinc.

For example, in the case where a hafnium oxide film is formed by adeposition apparatus using an ALD method, two kinds of gases, that is,ozone (O₃) as an oxidizer and a source gas which is obtained byvaporizing liquid containing a solvent and a hafnium precursor compound(e.g., a hafnium alkoxide or a hafnium amide such astetrakis(dimethylamide)hafnium (TDMAH)) are used. Note that the chemicalformula of tetrakis(dimethylamide)hafnium is Hf[N(CH₃)₂]₄. Examples ofanother material liquid include tetrakis(ethylmethylamide)hafnium.

For example, in the case where an aluminum oxide film is formed by adeposition apparatus using an ALD method, two kinds of gases, e.g., H₂Oas an oxidizer and a source gas which is obtained by vaporizing liquidcontaining a solvent and an aluminum precursor compound (e.g.,trimethylaluminum (TMA)) are used. Note that the chemical formula oftrimethylaluminum is Al(CH₃)₃. Examples of another material liquidinclude tris(dimethylamide)aluminum, triisobutylaluminum, and aluminumtris(2,2,6,6-tetramethyl-3,5-heptanedionate).

For example, in the case where a silicon oxide film is formed by adeposition apparatus using an ALD method, hexachlorodisilane is adsorbedon a surface where a film is to be formed, chlorine included in theadsorbate is removed, and radicals of an oxidizing gas (e.g., O₂ ordinitrogen monoxide) are supplied to react with the adsorbate.

For example, in the case where a tungsten film is formed with adeposition apparatus using an ALD method, a WF₆ gas and a B₂H₆ gas aresequentially introduced plural times to form an initial tungsten film,and then a WF₆ gas and an H₂ gas are used, so that a tungsten film isformed. Note that an SiH₄ gas may be used instead of a B₂H₆ gas.

For example, in the case where an oxide semiconductor film, e.g., anIn—Ga—Zn—O film is formed using a deposition apparatus using an ALDmethod, an In(CH₃)₃ gas and an O₃ gas) are sequentially introducedplural times to form an InO layer, a GaO layer is formed using aGa(CH₃)₃ gas and an O₃ gas), and then a ZnO layer is formed using aZn(CH₃)₂ gas and an O₃ gas). Note that the order of these layers is notlimited to this example. A mixed compound layer such as an In—Ga—Olayer, an In—Zn—O layer, or a Ga—Zn—O layer may be formed by mixingthese gases. Note that although an H₂O gas which is obtained by bubblingwater with an inert gas such as Ar may be used instead of an O₃ gas), itis preferable to use an O₃ gas), which does not contain H. Furthermore,instead of an In(CH₃)₃ gas, an In(C₂H₅)₃ gas may be used. Instead of aGa(CH₃)₃ gas, a Ga(C₂H₅)₃ gas may be used. Furthermore, a Zn(CH₃)₂ gasmay be used.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 3

In this embodiment, structures of a transistor that can be used in thedisplay panel of one embodiment of the present invention will bedescribed with reference to FIGS. 10A to 10C.

<Structure Example of Semiconductor Device>

FIG. 10A is a top view of the transistor 100. FIG. 10B is across-sectional view taken along the cutting plane line X1-X2 in FIG.10A, and FIG. 10C is a cross-sectional view taken along the cuttingplane line Y1-Y2 in FIG. 10A. Note that in FIG. 10A, some components ofthe transistor 100 (e.g., an insulating film serving as a gateinsulating film) are not illustrated to avoid complexity. Furthermore,the direction of the cutting plane line X1-X2 may be called a channellength direction, and the direction of the cutting plane line Y1-Y2 maybe called a channel width direction. As in FIG. 10A, some components arenot illustrated in some cases in top views of transistors describedbelow.

The transistor 100 can be used for the display panel described inEmbodiment 1, or other devices.

For example, when the transistor 100 is used as the transistor ME1, thesubstrate 102, the conductive film 104, a stacked film of the insulatingfilm 106 and the insulating film 107, the oxide semiconductor film 108,the conductive film 112 a, the conductive film 112 b, a stacked film ofthe insulating film 114 and the insulating film 116, the insulating film118, and a conductive film 120 b can be referred to as the substrate710, the conductive film 704, the insulating film 706, the semiconductorfilm 718, the conductive film 712A, the conductive film 712B, aninsulating film 721A, the insulating film 721B, and the conductive film720, respectively.

The transistor 100 includes the conductive film 104 functioning as afirst gate electrode over the substrate 102, the insulating film 106over the substrate 102 and the conductive film 104, the insulating film107 over the insulating film 106, the oxide semiconductor film 108 overthe insulating film 107, and the conductive films 112 a and 112 bfunctioning as source and drain electrodes electrically connected to theoxide semiconductor film 108, the insulating films 114 and 116 over theoxide semiconductor film 108 and the conductive films 112 a and 112 b, aconductive film 120 a that is over the insulating film 116 andelectrically connected to the conductive film 112 b, the conductive film120 b over the insulating film 116, and the insulating film 118 over theinsulating film 116 and the conductive films 120 a and 120 b.

The insulating films 106 and 107 function as a first gate insulatingfilm of the transistor 100. The insulating films 114 and 116 function asa second gate insulating film of the transistor 100. The insulating film118 functions as a protective insulating film of the transistor 100. Inthis specification and the like, the insulating films 106 and 107 arecollectively referred to as a first insulating film, the insulatingfilms 114 and 116 are collectively referred to as a second insulatingfilm, and the insulating film 118 is referred to as a third insulatingfilm in some cases.

The conductive film 120 b can be used as a second gate electrode of thetransistor 100.

In the case where the transistor 100 is used in a display panel, theconductive film 120 a can be used as an electrode of a display element,or the like.

The oxide semiconductor film 108 includes the oxide semiconductor film108 b (on the conductive film 104 side) that functions as a first gateelectrode, and an oxide semiconductor film 108 c over the oxidesemiconductor film 108 b. The oxide semiconductor films 108 b and 108 ccontain In, M (M is Al, Ga, Y, or Sn), and Zn.

The oxide semiconductor film 108 b preferably includes a region in whichthe atomic proportion of In is larger than the atomic proportion of M,for example. The oxide semiconductor film 108 c preferably includes aregion in which the atomic proportion of In is smaller than that in theoxide semiconductor film 108 b.

The oxide semiconductor film 108 b including the region in which theatomic proportion of In is larger than that of M can increase thefield-effect mobility (also simply referred to as mobility or μFE) ofthe transistor 100. Specifically, the field-effect mobility of thetransistor 100 can exceed 10 cm²/Vs, preferably exceed 30 cm²/Vs.

For example, the use of the transistor with high field-effect mobilityfor a gate driver that generates a gate signal (specifically, ademultiplexer connected to an output terminal of a shift registerincluded in a gate driver) allows a semiconductor device or a displaydevice to have a narrow frame.

On the other hand, the oxide semiconductor film 108 b including theregion in which the atomic proportion of In is larger than that of Mmakes it easier to change electrical characteristics of the transistor100 in light irradiation. However, in the semiconductor device of oneembodiment of the present invention, the oxide semiconductor film 108 cis formed over the oxide semiconductor film 108 b. Furthermore, theoxide semiconductor film 108 c including the region in which the atomicproportion of In is smaller than that in the oxide semiconductor film108 b has larger Eg than the oxide semiconductor film 108 b. For thisreason, the oxide semiconductor film 108 which is a layered structure ofthe oxide semiconductor film 108 b and the oxide semiconductor film 108c has high resistance to a negative bias stress test with lightirradiation.

Impurities such as hydrogen or moisture entering the channel region ofthe oxide semiconductor film 108, particularly the oxide semiconductorfilm 108 b adversely affect the transistor characteristics and thereforecause a problem. Moreover, it is preferable that the amount ofimpurities such as hydrogen or moisture in the channel region of theoxide semiconductor film 108 b be as small as possible. Furthermore,oxygen vacancies formed in the channel region in the oxide semiconductorfilm 108 b adversely affect the transistor characteristics and thereforecause a problem. For example, oxygen vacancies formed in the channelregion in the oxide semiconductor film 108 b are bonded to hydrogen toserve as a carrier supply source. The carrier supply source generated inthe channel region in the oxide semiconductor film 108 b causes a changein the electrical characteristics, typically, shift in the thresholdvoltage, of the transistor 100 including the oxide semiconductor film108 b. Therefore, it is preferable that the amount of oxygen vacanciesin the channel region of the oxide semiconductor film 108 b be as smallas possible.

In view of this, one embodiment of the present invention is a structurein which insulating films in contact with the oxide semiconductor film108, specifically the insulating film 107 formed under the oxidesemiconductor film 108 and the insulating films 114 and 116 formed overthe oxide semiconductor film 108 include excess oxygen. Oxygen or excessoxygen is transferred from the insulating film 107 and the insulatingfilms 114 and 116 to the oxide semiconductor film 108, whereby theoxygen vacancies in the oxide semiconductor film can be reduced. As aresult, a change in electrical characteristics of the transistor 100,particularly a change in the transistor 100 due to light irradiation,can be reduced.

In one embodiment of the present invention, a manufacturing method isused in which the number of manufacturing steps is not increased or anincrease in the number of manufacturing steps is extremely small,because the insulating film 107 and the insulating films 114 and 116 aremade to contain excess oxygen. Thus, the transistors 100 can bemanufactured with high yield.

Specifically, in a step of forming the oxide semiconductor film 108 b,the oxide semiconductor film 108 b is formed by a sputtering method inan atmosphere containing an oxygen gas, whereby oxygen or excess oxygenis added to the insulating film 107 over which the oxide semiconductorfilm 108 b is formed.

Furthermore, in a step of forming the conductive films 120 a and 120 b,the conductive films 120 a and 120 b are formed by a sputtering methodin an atmosphere containing an oxygen gas, whereby oxygen or excessoxygen is added to the insulating film 116 over which the conductivefilms 120 a and 120 b are formed. Note that in some cases, oxygen orexcess oxygen is added also to the insulating film 114 and the oxidesemiconductor film 108 under the insulating film 116 when oxygen orexcess oxygen is added to the insulating film 116.

<Oxide Conductor>

Next, an oxide conductor is described. In a step of forming theconductive films 120 a and 120 b, the conductive films 120 a and 120 bserve as a protective film for suppressing release of oxygen from theinsulating films 114 and 116. The conductive films 120 a and 120 b serveas semiconductors before a step of forming the insulating film 118 andserve as conductors after the step of forming the insulating film 118.

To allow the conductive films 120 a and 120 b to serve as conductors, anoxygen vacancy is formed in the conductive films 120 a and 120 b andhydrogen is added from the insulating film 118 to the oxygen vacancy,whereby a donor level is formed in the vicinity of the conduction band.As a result, the conductivity of each of the conductive films 120 a and120 b is increased, so that the oxide semiconductor film becomes aconductor. The conductive films 120 a and 120 b having become conductorscan each be referred to as oxide conductor. Oxide semiconductorsgenerally have a visible light transmitting property because of theirlarge energy gap. An oxide conductor is an oxide semiconductor having adonor level in the vicinity of the conduction band. Therefore, theinfluence of absorption due to the donor level is small in an oxideconductor, and an oxide conductor has a visible light transmittingproperty comparable to that of an oxide semiconductor.

<Components of the Semiconductor Device>

Components of the semiconductor device of this embodiment will bedescribed below in detail.

As materials described below, materials described in Embodiment 2 can beused.

The material that can be used for the substrate 102 described inEmbodiment 2 can be used for the substrate 102 in this embodiment.Furthermore, the materials that can be used for the insulating films 106and 107 described in Embodiment 2 can be used for the insulating films106 and 107 in this embodiment.

In addition, the materials that can be used for the conductive filmsfunctioning as the gate electrode, the source electrode, and the drainelectrode described in Embodiment 2 can be used for the conductive filmsfunctioning as the first gate electrode, the source electrode, and thedrain electrode in this embodiment.

<<Oxide Semiconductor Film>>

The oxide semiconductor film 108 can be formed using the materialsdescribed above.

In the case where the oxide semiconductor film 108 b includes In-M-Znoxide, it is preferable that the atomic ratio of metal elements of asputtering target used for forming the In-M-Zn oxide satisfy In>M Theatomic ratio between metal elements in such a sputtering target is, forexample, In:M:Zn=2:1:3, In:M:Zn=3:1:2, or In:M:Zn=4:2:4.1.

In the case where the oxide semiconductor film 108 c is In-M-Zn oxide,it is preferable that the atomic ratio of metal elements of a sputteringtarget used for forming a film of the In-M-Zn oxide satisfy In Theatomic ratio of metal elements in such a sputtering target is, forexample, In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, In:M:Zn=1:3:2, In:M:Zn=1:3:4,In:M:Zn=1:3:6, or In:M:Zn=1:4:5.

In the case where the oxide semiconductor films 108 b and 108 c areformed of In-M-Zn oxide, it is preferable to use a target includingpolycrystalline In-M-Zn oxide as the sputtering target. The use of thetarget including polycrystalline In-M-Zn oxide facilitates formation ofthe oxide semiconductor films 108 b and 108 c having crystallinity. Notethat the atomic ratios of metal elements in each of the formed oxidesemiconductor films 108 b and 108 c vary from the above atomic ratio ofmetal elements of the sputtering target within a range of ±40% as anerror. For example, when a sputtering target of the oxide semiconductorfilm 108 b with an atomic ratio of In to Ga and Zn of 4:2:4.1 is used,the atomic ratio of In to Ga and Zn in the oxide semiconductor film 108b may be 4:2:3 or in the vicinity of 4:2:3.

The energy gap of the oxide semiconductor film 108 is 2 eV or more,preferably 2.5 eV or more, further preferably 3 eV or more. The use ofan oxide semiconductor having a wide energy gap can reduce off-statecurrent of the transistor 100. In particular, an oxide semiconductorfilm having an energy gap more than or equal to 2 eV, preferably morethan or equal to 2 eV and less than or equal to 3.0 eV is preferablyused as the oxide semiconductor film 108 b, and an oxide semiconductorfilm having an energy gap more than or equal to 2.5 eV and less than orequal to 3.5 eV is preferably used as the oxide semiconductor film 108c. Furthermore, the oxide semiconductor film 108 c preferably has ahigher energy gap than the oxide semiconductor film 108 b.

Each thickness of the oxide semiconductor film 108 b and the oxidesemiconductor film 108 c is more than or equal to 3 nm and less than orequal to 200 nm, preferably more than or equal to 3 nm and less than orequal to 100 nm, more preferably more than or equal to 3 nm and lessthan or equal to 50 nm.

An oxide semiconductor film with low carrier density is used as theoxide semiconductor film 108 c. For example, the carrier density of theoxide semiconductor film 108 c is lower than or equal to 1×10¹⁷ /cm³,preferably lower than or equal to 1×10¹⁵ /cm³, further preferably lowerthan or equal to 1×10¹³ /cm³, still further preferably lower than orequal to 1×10¹¹ /cm³.

Note that, without limitation to the compositions and materialsdescribed above, a material with an appropriate composition may be useddepending on required semiconductor characteristics and electricalcharacteristics (e.g., field-effect mobility and threshold voltage) of atransistor. Furthermore, in order to obtain required semiconductorcharacteristics of a transistor, it is preferable that the carrierdensity, the impurity concentration, the defect density, the atomicratio of a metal element to oxygen, the interatomic distance, thedensity, and the like of the oxide semiconductor film 108 b and theoxide semiconductor film 108 c be set to be appropriate.

Note that it is preferable to use, as the oxide semiconductor film 108 band the oxide semiconductor film 108 c, an oxide semiconductor film inwhich the impurity concentration is low and the density of defect statesis low, in which case the transistor can have more excellent electricalcharacteristics. Here, the state in which the impurity concentration islow and the density of defect states is low (the amount of oxygenvacancy is small) is referred to as “highly purified intrinsic” or“substantially highly purified intrinsic”. A highly purified intrinsicor substantially highly purified intrinsic oxide semiconductor film hasfew carrier generation sources, and thus can have a low carrier density.Thus, a transistor in which a channel region is formed in the oxidesemiconductor film rarely has a negative threshold voltage (is rarelynormally on). A highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor film has a low density of defectstates and accordingly has few carrier traps in some cases. Furthermore,the highly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film has an extremely low off-state current; evenwhen an element has a channel width of 1×10⁶ μm and a channel length of10 μm, the off-state current can be less than or equal to themeasurement limit of a semiconductor parameter analyzer, that is, lessthan or equal to 1×10⁻¹³ A, at a voltage (drain voltage) between asource electrode and a drain electrode of from 1 V to 10 V.

Accordingly, the transistor in which the channel region is formed in thehighly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film can have a small change in electricalcharacteristics and high reliability. Charges trapped by the trap statesin the oxide semiconductor film take a long time to be released and maybehave like fixed charges. Thus, the transistor whose channel region isformed in the oxide semiconductor film having a high density of trapstates has unstable electrical characteristics in some cases. Asexamples of the impurities, hydrogen, nitrogen, alkali metal, andalkaline earth metal are given.

Hydrogen included in the oxide semiconductor film reacts with oxygenbonded to a metal atom to be water, and also causes oxygen vacancy in alattice from which oxygen is released (or a portion from which oxygen isreleased). Due to entry of hydrogen into the oxygen vacancy, an electronserving as a carrier is generated in some cases. Furthermore, in somecases, bonding of part of hydrogen to oxygen bonded to a metal atomcauses generation of an electron serving as a carrier. Thus, atransistor including an oxide semiconductor film which contains hydrogenis likely to be normally on. Accordingly, it is preferable that hydrogenbe reduced as much as possible in the oxide semiconductor film 108.Specifically, in the oxide semiconductor film 108, the concentration ofhydrogen which is measured by SIMS is lower than or equal to 2×10²⁰atoms/cm³, preferably lower than or equal to 5×10¹⁹ atoms/cm³, furtherpreferably lower than or equal to 1×10¹⁹ atoms/cm³, further preferablylower than or equal to 5×10¹⁸ atoms/cm³, further preferably lower thanor equal to 1×10¹⁸ atoms/cm³, further preferably lower than or equal to5×10¹⁷ atoms/cm³, and further preferably lower than or equal to 1×10¹⁶atoms/cm³.

The oxide semiconductor film 108 b preferably includes a region in whichhydrogen concentration is smaller than that in the oxide semiconductorfilm 108 c. A semiconductor device including the oxide semiconductorfilm 108 b having the region in which hydrogen concentration is smallerthan that in the oxide semiconductor film 108 c can be increased inreliability.

When silicon or carbon that is one of elements belonging to Group 14 isincluded in the oxide semiconductor film 108 b, oxygen vacancy increasesin the oxide semiconductor film 108 b, and the oxide semiconductor film108 b becomes an n-type film. Thus, the concentration of silicon orcarbon (the concentration is measured by SIMS) in the oxidesemiconductor film 108 b or the concentration of silicon or carbon (theconcentration is measured by SIMS) in the vicinity of an interface withthe oxide semiconductor film 108 b is set to be lower than or equal to2×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁷ atoms/cm³.

In addition, the concentration of alkali metal or alkaline earth metalof the oxide semiconductor film 108 b, which is measured by SIMS, islower than or equal to 1×10¹⁸ atoms/cm³, preferably lower than or equalto 2×10¹⁶ atoms/cm³. Alkali metal and alkaline earth metal mightgenerate carriers when bonded to an oxide semiconductor, in which casethe off-state current of the transistor might be increased. Therefore,it is preferable to reduce the concentration of alkali metal or alkalineearth metal of the oxide semiconductor film 108 b.

Furthermore, when including nitrogen, the oxide semiconductor film 108 beasily becomes n-type by generation of electrons serving as carriers andan increase of carrier density. Thus, a transistor including an oxidesemiconductor film which contains nitrogen is likely to have normally-oncharacteristics. For this reason, nitrogen in the oxide semiconductorfilm is preferably reduced as much as possible; the concentration ofnitrogen which is measured by SIMS is preferably set to be, for example,lower than or equal to 5×10¹⁸ atoms/cm³.

The oxide semiconductor film 108 b and the oxide semiconductor film 108c may have a non-single-crystal structure, for example. The non-singlecrystal structure includes a c-axis aligned crystalline oxidesemiconductor (CAAC-OS), a polycrystalline structure, a microcrystallinestructure, or an amorphous structure, for example. Among the non-singlecrystal structure, the amorphous structure has the highest density ofdefect states, whereas CAAC-OS has the lowest density of defect states.

<<Insulating Films Functioning as Second Gate Insulating Film>>

The insulating films 114 and 116 function as a second gate insulatingfilm of the transistor 100. In addition, the insulating films 114 and116 each have a function of supplying oxygen to the oxide semiconductorfilm 108. That is, the insulating films 114 and 116 contain oxygen.Furthermore, the insulating film 114 is an insulating film which cantransmit oxygen. Note that the insulating film 114 also functions as afilm which relieves damage to the oxide semiconductor film 108 at thetime of forming the insulating film 116 in a later step.

For example, the insulating films 114 and 116 described in Embodiment 2can be used as the insulating films 114 and 116 in this embodiment.

<<Oxide Semiconductor Film Functioning as Conductive Film, OxideSemiconductor Film Functioning as Second Gate Electrode>>

The material of the oxide semiconductor film 108 described above can beused for the conductive film 120 a and the conductive film 120 bfunctioning as the second gate electrode.

That is, the conductive film 120 a and the conductive film 120 bfunctioning as a second gate electrode contain a metal element which isthe same as that contained in the oxide semiconductor film 108 (theoxide semiconductor film 108 b and the oxide semiconductor film 108 c).For example, the conductive film 120 b functioning as a second gateelectrode and the oxide semiconductor film 108 (the oxide semiconductorfilm 108 b and the oxide semiconductor film 108 c) contain the samemetal element; thus, the manufacturing cost can be reduced.

For example, in the case where the conductive film 120 a and theconductive film 120 b functioning as a second gate electrode are eachIn-M-Zn oxide, the atomic ratio of metal elements in a sputtering targetused for forming the In-M-Zn oxide preferably satisfies In M The atomicratio of metal elements in such a sputtering target is In:M:Zn=2:1:3,In:M:Zn=3:1:2, In:M:Zn=4:2:4.1, or the like.

The conductive film 120 a and the conductive film 120 b functioning as asecond gate electrode can each have a single-layer structure or astacked-layer structure of two or more layers. Note that in the casewhere the conductive film 120 a and the conductive film 120 b each havea stacked-layer structure, the composition of the sputtering target isnot limited to that described above.

<<Insulating Film Functioning as Protective Insulating Film ofTransistor>>

The insulating film 118 serves as a protective insulating film of thetransistor 100.

The insulating film 118 includes one or both of hydrogen and nitrogen.Alternatively, the insulating film 118 includes nitrogen and silicon.The insulating film 118 has a function of blocking oxygen, hydrogen,water, alkali metal, alkaline earth metal, or the like. It is possibleto prevent outward diffusion of oxygen from the oxide semiconductor film108, outward diffusion of oxygen included in the insulating films 114and 116, and entry of hydrogen, water, or the like into the oxidesemiconductor film 108 from the outside by providing the insulating film118.

The insulating film 118 has a function of supplying one or both ofhydrogen and nitrogen to the conductive film 120 a and the conductivefilm 120 b functioning as a second gate electrode. The insulating film118 preferably includes hydrogen and has a function of supplying thehydrogen to the conductive films 120 a and 120 b. The conductive films120 a and 120 b supplied with hydrogen from the insulating film 118function as conductors.

A nitride insulating film, for example, can be used as the insulatingfilm 118. The nitride insulating film is formed using silicon nitride,silicon nitride oxide, aluminum nitride, aluminum nitride oxide, or thelike.

Although the variety of films such as the conductive films, theinsulating films, and the oxide semiconductor films which are describedabove can be formed by a sputtering method or a PECVD method, such filmsmay be formed by another method, e.g., a thermal CVD method. Examples ofthe thermal CVD method include an MOCVD method and an ALD method.Specifically, the methods described in Embodiment 2 can be used.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 4

In this embodiment, a structure of an input/output device of oneembodiment of the present invention will be described with reference toFIG. 11.

FIG. 11 is an exploded view illustrating a structure of an input/outputdevice 800.

The input/output device 800 is provided with a display panel 806 and atouch sensor 804 including a region overlapping with the display panel806. Note that the input/output device 800 can be a touch panel.

The input/output device 800 is provided with a driver circuit 810 fordriving the touch sensor 804 and the display panel 806, a battery 811for supplying power to the driver circuit 810, and a housing where thetouch sensor 804, the display panel 806, the driver circuit 810, and thebattery 811 are stored.

<<Touch Sensor 804>>

The touch sensor 804 includes the region overlapping with the displaypanel 806. Note that an FPC 803 is electrically connected to the touchsensor 804.

For the touch sensor 804, a resistive touch sensor, a capacitive touchsensor, or a touch sensor using a photoelectric conversion element canbe used, for example.

Note that the touch sensor 804 may be used as part of the display panel806.

<<Display Panel 806>>

The display panel described in Embodiment 1 can be used as the displaypanel 806, for example. Note that an FPC 805 is electrically connectedto the display panel 806.

<<Driver Circuit 810>>

As the driver circuit 810, a power supply circuit or a signal processingcircuit can be used, for example. Power supplied from the battery or anexternal commercial power supply can be utilized.

The signal processing circuit has a function of outputting a videosignal and a clock signal.

The power supply circuit has a function of supplying predeterminedpower.

<<Housing>>

An upper cover 801, a lower cover 802 which fits the upper cover 801,and a frame 809 which is stored in a region surrounded by the uppercover 801 and the lower cover 802 can be used for the housing, forexample.

The frame 809 has a function of protecting the display panel 806, afunction of blocking electromagnetic waves generated by the operation ofthe driver circuit 810, or a function of a heat sink.

Metal, a resin, an elastomer, or the like can be used for the uppercover 801, the lower cover 802, or the frame 809.

<<Battery 811>>

The battery 811 has a function of supplying power.

Note that a member such as a polarizing plate, a retardation plate, or aprism sheet can be used for the input/output device 800.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 5

In this embodiment, a structure of an information processing device ofone embodiment of the present invention will be described with referenceto FIGS. 12A and 12B, FIGS. 13A to 13D, FIGS. 14A and 14B, and FIG. 15.

FIG. 12A is a block diagram illustrating a structure of an informationprocessing device 200. FIG. 12B is a projection view illustrating anexample of an external view of the information processing device 200.

FIG. 13A is a block diagram illustrating a configuration of a displayportion 230. FIG. 13B is a block diagram illustrating a configuration ofa display portion 230B. FIGS. 13C and 13D are circuit diagrams eachillustrating a configuration of a pixel 232(i, j).

<Configuration Example of Information Processing Device>

The information processing device 200 described in this embodimentincludes an arithmetic device 210 and an input/output device 220 (seeFIG. 12A).

The arithmetic device 210 is configured to receive positionalinformation P1 and supply image information V and control information.

The input/output device 220 is configured to supply the positionalinformation P1 and receive the image information V and the controlinformation.

The input/output device 220 includes the display portion 230 thatdisplays the image information V and an input portion 240 that suppliesthe positional information P1.

The display portion 230 includes a first display element and a seconddisplay element overlapping with the first display element. The displayportion 230 further includes a first pixel circuit for driving the firstdisplay element and a second pixel circuit for driving the seconddisplay element.

The input portion 240 is configured to detect the position of a pointerand supply the positional information P1 determined in accordance withthe position.

The arithmetic device 210 is configured to determine the moving speed ofthe pointer in accordance with the positional information P1.

The arithmetic device 210 is configured to determine the contrast orbrightness of the image information V in accordance with the movingspeed.

The information processing device 200 described in this embodimentincludes the input/output device 220 that supplies the positionalinformation P1 and receives the image information V and the arithmeticdevice 210 that receives the positional information P1 and supplies theimage information V. The arithmetic device 210 is configured todetermine the contrast or brightness of the image information V inaccordance with the moving speed of the positional information P1.

With this structure, eyestrain on a user caused when the displayposition of image information is moved can be reduced, that is,eye-friendly display can be achieved. Moreover, the power consumptioncan be reduced and excellent visibility can be provided even in a brightplace exposed to direct sunlight, for example. Thus, the novelinformation processing device that is highly convenient or reliable canbe provided.

<Configuration>

The information processing device of one embodiment of the presentinvention includes the arithmetic device 210 or the input/output device220.

<<Arithmetic Device 210>>

The arithmetic device 210 includes an arithmetic portion 211 and amemory portion 212. The arithmetic device 210 further includes atransmission path 214 and an input/output interface 215 (see FIG. 12A).

<<Arithmetic Portion 211>>

The arithmetic portion 211 is configured to, for example, execute aprogram. For example, a CPU described in Embodiment 6 can be used. Inthat case, power consumption can be sufficiently reduced.

<<Memory Portion 212>>

The memory portion 212 is configured to, for example, store the programexecuted by the arithmetic portion 211, initial information, settinginformation, an image, or the like.

Specifically, a hard disk, a flash memory, a memory including atransistor including an oxide semiconductor, or the like can be used forthe memory portion 212.

<<Input/Output Interface 215, Transmission Path 214>>

The input/output interface 215 includes a terminal or a wiring and isconfigured to supply and receive information. For example, theinput/output interface 215 can be electrically connected to thetransmission path 214 and the input/output device 220.

The transmission path 214 includes a wiring and is configured to supplyand receive information. For example, the transmission path 214 can beelectrically connected to the input/output interface 215. In addition,the transmission path 214 can be electrically connected to thearithmetic portion 211 or the memory portion 212.

<<Input/Output Device 220>>

The input/output device 220 includes the display portion 230, the inputportion 240, a sensor portion 250, or a communication portion 290.

<<Display Portion 230>>

The display portion 230 includes a display region 231, a driver circuitGD, and a driver circuit SD (see FIG. 13A). For example, the displaypanel described in Embodiment 1 can be used. In that case, powerconsumption can be reduced.

The display region 231 includes a plurality of pixels 232(i, 1) to 232(i, n) arranged in the row direction, a plurality of pixels 232(1, j) to232 (m, j) arranged in the column direction, a scan line G(i)electrically connected to the pixels 232(i, 1) to 232 (i, n), a signalline S(j) electrically connected to the pixels 232(1, j) to 232 (m, j),and a wiring VCOM. Note that i is an integer greater than or equal to 1and less than or equal to m, j is an integer greater than or equal to 1and less than or equal to n, and each of m and n is an integer greaterthan or equal to 1.

Note that the pixel 232(i, j) includes a portion 232(i, j)1 provided inthe first display portion and a portion 232(i, j)2 provided in thesecond display portion (see FIGS. 13C and 13D). The portion 232(i, j)1provided in the first display portion is electrically connected to ascan line G(i)1, a signal line S(j)1, and a wiring VCOM1. The portion232(i, j)2 provided in the second display portion is electricallyconnected to a scan line G(i)2, a signal line S(j)2, a wiring VCOM2, anda wiring ANO. The scan line G(i) includes the scan line G(i)1 and thescan line G(i)2, and the signal line S(j) includes the signal line S(j)1and the signal line S(j)2.

The display portion can include a plurality of driver circuits. Forexample, the display portion 230B can include a driver circuit GDA and adriver circuit GDB (see FIG. 13B).

<<Driver Circuit GD>>

The driver circuit GD is configured to supply a selection signal inaccordance with the control information.

For example, the driver circuit GD is configured to supply a selectionsignal to one scan line at a frequency of 30 Hz or higher, preferably 60Hz or higher, in accordance with the control information. Accordingly,moving images can be smoothly displayed.

For example, the driver circuit GD is configured to supply a selectionsignal to one scan line at a frequency of lower than 30 Hz, preferablylower than 1 Hz, more preferably less than once per minute, inaccordance with the control information. Accordingly, a still image canbe displayed while flickering is suppressed.

For example, in the case where a plurality of driver circuits isprovided, the driver circuits GDA and GDB may supply the selectionsignals at different frequencies. Specifically, the selection signal canbe supplied at a higher frequency to a region on which moving images aresmoothly displayed than to a region on which a still image is displayedin a state where flickering is suppressed.

<<Driver Circuit SD>>

The driver circuit SD is configured to supply an image signal inaccordance with the image information V.

<<Pixel 232(i,j)>>

The pixel 232(i, j) includes a first display element 235LC and a seconddisplay element 235EL overlapping with the first display element 235LC.The pixel 232(i, j) further includes the first pixel circuit for drivingthe first display element 235LC and the second pixel circuit for drivingthe second display element 235EL (see FIGS. 13C and 13D).

<<First Display Element 235LC>>

For example, a display element having a function of controlling lighttransmission can be used as the first display element 235LC.Specifically, a polarizing plate and a liquid crystal element, a MEMSshutter display element, or the like can be used.

Specifically, a liquid crystal element driven in any of the followingdriving modes can be used: an in-plane switching (IPS) mode, a twistednematic (TN) mode, a fringe field switching (FFS) mode, an axiallysymmetric aligned micro-cell (ASM) mode, an optically compensatedbirefringence (OCB) mode, a ferroelectric liquid crystal (FLC) mode, anantiferroelectric liquid crystal (AFLC) mode, and the like.

In addition, a liquid crystal element that can be driven by, forexample, a vertical alignment (VA) mode such as a multi-domain verticalalignment (MVA) mode, a patterned vertical alignment (PVA) mode, anelectrically controlled birefringence (ECB) mode, a continuous pinwheelalignment (CPA) mode, or an advanced super view (ASV) mode can be used.

The first display element 235LC includes a first electrode, a secondelectrode, and a liquid crystal layer. The liquid crystal layer containsa liquid crystal material whose orientation is controlled by voltageapplied between the first electrode and the second electrode. Forexample, the orientation of the liquid crystal material can becontrolled by an electric field in the thickness direction (alsoreferred to as the vertical direction), the horizontal direction, or thediagonal direction of the liquid crystal layer.

For example, thermotropic liquid crystal, low-molecular liquid crystal,high-molecular liquid crystal, polymer dispersed liquid crystal,ferroelectric liquid crystal, or anti-ferroelectric liquid crystal canbe used. These liquid crystal materials exhibit a cholesteric phase, asmectic phase, a cubic phase, a chiral nematic phase, an isotropicphase, or the like depending on conditions. Alternatively, a liquidcrystal material which exhibits a blue phase can be used.

<<Second Display Element 235EL>>

A display element having a function of emitting light can be used as thesecond display element 235EL, for example. Specifically, an organic ELelement can be used as the second display element 235EL.

More specifically, an organic EL element which emits white light can beused as the second display element 235EL. Alternatively, an organic ELelement which emits blue light, green light, or red light can be used asthe second display element 235EL.

<<Pixel Circuit>>

The configuration of the pixel circuit can be designed according to thedisplay element.

For example, a driver circuit which is electrically connected to thescan line G(i)1, the signal line S(j)1, and the wiring VCOM1 and drivesa liquid crystal element is described (see FIG. 13C).

A switch, the capacitor C1, and the like can be used in the pixelcircuit. Alternatively, for example, a transistor, a diode, a resistor,or an inductor can be used in the pixel circuit.

For example, a plurality of transistors can be used as a switch.Alternatively, a plurality of transistors connected in parallel, inseries, or in combination of parallel connection and series connectioncan be used as a switch.

For example, a capacitor may be formed by the first electrode of thefirst display element 235LC and a conductive film having a regionoverlapping with the first electrode.

For example, the pixel circuit includes a transistor SW functioning as aswitch, the first display element 235LC, and the capacitor C1. A gateelectrode of the transistor SW is electrically connected to the scanline G(i)1, and a first electrode of the transistor SW is electricallyconnected to the signal line S(j)1. The first electrode of the firstdisplay element 235LC is electrically connected to a second electrode ofthe transistor SW, and a second electrode of the first display element235LC is electrically connected to the wiring VCOM1. A first electrodeof the capacitor C1 is electrically connected to the second electrode ofthe transistor SW, and a second electrode of the capacitor C1 iselectrically connected to the wiring VCOM1.

Here, for example, a driver circuit which is electrically connected tothe scan line G(i)2, the signal line S(j)2, the wiring VCOM2, and thewiring ANO and drives an organic EL element is described (see FIG. 13D).

For example, the pixel circuit includes a transistor SW2 functioning asa switch, a capacitor C2, a transistor M, and the second display element235EL. A gate electrode of the transistor SW2 is electrically connectedto the scan line G(i)2, and a first electrode of the transistor SW2 iselectrically connected to the signal line S(j)2. A first electrode ofthe capacitor C2 is electrically connected to a second electrode of thetransistor SW2, and a second electrode of the capacitor C2 iselectrically connected to the wiring ANO. A gate electrode of thetransistor M is electrically connected to the transistor SW2, and afirst electrode of the transistor M is electrically connected to thewiring ANO. A first electrode of the second display element 235EL iselectrically connected to a second electrode of the transistor M, and asecond electrode of the second display element 235EL is electricallyconnected to the wiring VCOM2 (see FIG. 13D).

<<Transistor>>

For example, semiconductor films formed at the same step can be used fortransistors in the driver circuit and the pixel circuit.

As the transistors in the driver circuit and the pixel circuit,bottom-gate transistors, top-gate transistors, or the like can be used.

A manufacturing line for a bottom-gate transistor including amorphoussilicon as a semiconductor can be easily remodeled into a manufacturingline for a bottom-gate transistor including an oxide semiconductor as asemiconductor, for example. Furthermore, for example, a manufacturingline for a top-gate transistor including polysilicon as a semiconductorcan be easily remodeled into a manufacturing line for a top-gatetransistor including an oxide semiconductor as a semiconductor.

For example, a transistor including a semiconductor containing anelement of Group 4 can be used. Specifically, a semiconductor containingsilicon can be used for a semiconductor film. For example, singlecrystal silicon, polysilicon, microcrystalline silicon, or amorphoussilicon can be used for the semiconductor film of the transistor.

Note that the temperature for forming a transistor using polysilicon ina semiconductor film is lower than the temperature for forming atransistor using single crystal silicon in a semiconductor film.

In addition, the transistor using polysilicon in a semiconductor filmhas higher field-effect mobility than the transistor using amorphoussilicon in a semiconductor film, and therefore a pixel including thetransistor using polysilicon can have a high aperture ratio. Moreover,pixels arranged at high resolution, a gate driver circuit, and a sourcedriver circuit can be formed over the same substrate. As a result, thenumber of components included in an electronic device can be reduced.

In addition, the transistor using polysilicon in a semiconductor filmhas higher reliability than the transistor using amorphous silicon in asemiconductor film

For example, a transistor including an oxide semiconductor can be used.Specifically, an oxide semiconductor containing indium or an oxidesemiconductor containing indium, gallium, and zinc can be used for asemiconductor film.

For example, a transistor having a lower leakage current in an off statethan a transistor that uses amorphous silicon for a semiconductor filmcan be used. Specifically, a transistor that uses an oxide semiconductorfor a semiconductor film can be used.

A pixel circuit in the transistor that uses an oxide semiconductor forthe semiconductor film can hold an image signal for a longer time than apixel circuit in a transistor that uses amorphous silicon for asemiconductor film. Specifically, the selection signal can be suppliedat a frequency of lower than 30 Hz, preferably lower than 1 Hz, morepreferably less than once per minute while flickering is suppressed.Consequently, eyestrain on a user of the information processing devicecan be reduced, and power consumption for driving can be reduced.

Alternatively, for example, a transistor including a compoundsemiconductor can be used. Specifically, a semiconductor containinggallium arsenide can be used for a semiconductor film.

For example, a transistor including an organic semiconductor can beused.

Specifically, an organic semiconductor containing any of polyacenes andgraphene can be used for the semiconductor film.

<<Input Portion 240>>

A variety of human interfaces or the like can be used as the inputportion 240 (see FIG. 12A).

For example, a keyboard, a mouse, a touch sensor, a microphone, acamera, or the like can be used as the input portion 240. Note that atouch sensor having a region overlapping with the display portion 230can also be used. An input/output device that includes the displayportion 230 and the touch sensor having a region overlapping with thedisplay portion 230 can be referred to as a touch panel.

For example, a user can make various gestures (e.g., tap, drag, swipe,and pinch in) using his/her finger as a pointer on the touch panel.

The arithmetic device 210, for example, analyzes information on theposition, track, or the like of the finger on the touch panel anddetermines that a specific gesture is supplied when the analysis resultsmeet predetermined conditions. Therefore, the user can supply a certainoperation instruction associated with a certain gesture by using thegesture.

For instance, the user can supply a “scrolling instruction” for changinga portion where image information is displayed by using a gesture oftouching and moving his/her finger on the touch panel.

<<Sensor Portion 250>>

The sensor portion 250 is configured to acquire information P2 bydetecting the surrounding state.

For example, a camera, an acceleration sensor, a direction sensor, apressure sensor, a temperature sensor, a humidity sensor, an illuminancesensor, or a global positioning system (GPS) signal receiving circuitcan be used as the sensor portion 250.

For example, in the case where the arithmetic device 210 determines thatthe surrounding brightness sensed by an illuminance sensor of the sensorportion 250 is sufficiently higher than predetermined brightness, imageinformation is displayed on the first display portion. In the case wherethe arithmetic device 210 determines that the surrounding brightness islow, image information is displayed on the second display portion.Alternatively, image information is displayed on the first displayportion and the second display portion.

Specifically, in the case where the arithmetic device 210 determinesthat the surrounding brightness is sufficiently high, an image isdisplayed with a reflective liquid crystal element, and in the casewhere the arithmetic device 210 determines that the surroundingbrightness is low, an image is displayed with an organic EL element.

Thus, image information can be displayed in such a manner that, forexample, a reflective display element is used in an environment withstrong external light and a self-luminous display element is used in adim environment. As a result, a novel information processing device thathas low power consumption and is highly convenient or reliable can beprovided.

<<Communication Portion 290>>

The communication portion 290 is configured to supply and acquireinformation to/from a network.

<<Program>>

A program of one embodiment of the present invention will be describedwith reference to FIGS. 14A and 14B and FIG. 15.

FIG. 14A is a flow chart showing main processing of the program of oneembodiment of the present invention, and FIG. 14B is a flow chartshowing interrupt processing.

FIG. 15 schematically illustrates a method for displaying imageinformation on the display portion 230.

The program of one embodiment of the present invention has the followingsteps (see FIG. 14A).

In a first step, setting is initialized (see (51) in FIG. 14A).

For instance, predetermined image information and the second mode can beused for the initialization.

For example, a still image can be used as the predetermined imageinformation.

Alternatively, a mode in which the selection signal is supplied at afrequency of lower than 30 Hz, preferably lower than 1 Hz, morepreferably less than once per minute can be used as the second mode. Forexample, in the case where the time is displayed on the informationprocessing device on the second time scale, a mode in which theselection signal is supplied at a frequency of 1 Hz can be used as thesecond mode. In the case where the time is displayed on the informationprocessing device on the minute time scale, a mode in which theselection signal is supplied once per minute can be used as the secondmode.

In a second step, interrupt processing is allowed (see S2 in FIG. 14A).Note that an arithmetic device allowed to execute the interruptprocessing can perform the interrupt processing in parallel with themain processing. The arithmetic device which has returned from theinterrupt processing to the main processing can reflect the results ofthe interrupt processing in the main processing.

The arithmetic device may execute the interrupt processing when acounter has an initial value, and the counter may be set at a valueother than the initial value when the arithmetic device returns from theinterrupt processing. Thus, the interrupt processing is ready to beexecuted after the program is started up.

In a third step, image information is displayed in a mode selected inthe first step or the interrupt processing (see S3 in FIG. 14A).

For instance, predetermined image information is displayed in the secondmode, in accordance with the initialization.

Specifically, the predetermined image information is displayed in a modein which the selection signal is supplied to one scan line at afrequency of lower than 30 Hz, preferably lower than 1 Hz, morepreferably less than once per minute.

For example, the selection signal is supplied at Time T1 so that firstimage information PIC1 is displayed on the display portion 230 (see FIG.15). At Time T2, which is, for example, one second after Time T1, theselection signal is supplied so that the predetermined image informationis displayed.

Alternatively, in the case where a predetermined event is not suppliedin the interrupt processing, image information is displayed in thesecond mode.

For example, the selection signal is supplied at Time T5 so that fourthimage information PIC4 is displayed on the display portion 230. At TimeT6, which is, for example, one second after Time T5, the selectionsignal is supplied so that the same image information is displayed. Notethat the length of a period from Time T5 to Time T6 can be equal to thatof a period from Time T1 to Time T2.

For instance, in the case where the predetermined event is supplied inthe interrupt processing, predetermined image information is displayedin the first mode.

Specifically, in the case where an event associated with a “page turninginstruction” is supplied in the interrupt processing, image informationis switched from one to another in a mode in which the selection signalis supplied to one scan line at a frequency of 30 Hz or higher,preferably 60 Hz or higher.

Alternatively, in the case where an event associated with the “scrollinginstruction” is supplied in the interrupt processing, second imageinformation PIC2, which includes part of the displayed first imageinformation PIC1 and the following part, is displayed in a mode in whichthe selection signal is supplied to one scan line at a frequency of 30Hz or higher, preferably 60 Hz or higher.

Thus, a moving image can be displayed smoothly by switching images inaccordance with the “page tuning instruction,” for example.Alternatively, a moving image in which an image is gradually moved inaccordance with the “scrolling instruction” can be displayed smoothly.

Specifically, the selection signal is supplied at Time T3 after theevent associated with the “scrolling instruction” is supplied so thatthe second image information PIC2 whose display position and the likeare changed from those of the first image information PIC1 is displayed(see FIG. 15). The selection signal is supplied at Time T4 so that thirdimage information PIC3 whose display position and the like are changedfrom those of the second image information PIC2 is displayed. Note thateach of a period from Time T2 to Time T3, a period from Time T3 to TimeT4, and a period from Time T4 to Time T5 is shorter than the period fromTime T1 to Time T2.

In the fourth step, the program moves to the fifth step when atermination instruction is supplied, and the program moves to the thirdstep when the termination instruction is not supplied (see S4 in FIG.14A).

Note that in the interrupt processing, for example, the terminationinstruction can be supplied.

In the fifth step, the program terminates (see S5 in FIG. 14A).

The interrupt processing includes sixth to eighth steps described below(see FIG. 14B).

In the sixth step, the processing proceeds to the seventh step when apredetermined event has been supplied, whereas the processing proceedsto the eighth step when the predetermined event has not been supplied(see S6 in FIG. 14B).

For example, whether the predetermined event is supplied in apredetermined period or not can be a branch condition. Specifically, thepredetermined period can be longer than 0 seconds and shorter than orequal to 5 seconds, preferably shorter than or equal to 1 second,further preferably shorter than or equal to 0.5 seconds, still furtherpreferably shorter than or equal to 0.1 seconds.

For example, the predetermined event can include an event associatedwith the termination instruction.

In the seventh step, the mode is changed (see S7 in FIG. 14B).Specifically, the mode is changed to the second mode when the first modehas been selected, or the mode is changed to the first mode when thesecond mode has been selected.

In the eighth step, the interrupt processing terminates (see S8 in FIG.14B).

<<Predetermined Event>>

A variety of instructions can be associated with a variety of events.

The following instructions can be given as examples: “page-turninginstruction” for switching displayed image information from one toanother and “scroll instruction” for moving the display position of partof image information and displaying another part continuing from thatpart.

For example, the following events can be used: events supplied using apointing device such as a mouse (e.g., “click” and “drag”) and eventssupplied to a touch panel with a finger or the like used as a pointer(e.g., “tap”, “drag”, and “swipe”).

For example, the position of a slide bar pointed by a pointer, the swipespeed, and the drag speed can be used as arguments assigned to aninstruction associated with the predetermined event.

Specifically, a parameter that determines the page-turning speed or thelike can be used to execute the “page-turning instruction,” and aparameter that determines the moving speed of the display position orthe like can be used to execute the “scroll instruction.”

For example, the display brightness, contrast, or saturation may bechanged in accordance with the page-turning speed and/or the scrollspeed.

Specifically, in the case where the page-turning speed and/or the scrollspeed are/is higher than the predetermined speed, the display brightnessmay be decreased in synchronization with the speed.

Alternatively, in the case where the page-turning speed and/or thescroll speed are/is higher than the predetermined speed, the contrastmay be decreased in synchronization with the speed.

For example, the speed at which user's eyes cannot follow displayedimages can be used as the predetermined speed.

The contrast can be reduced in such a manner that the gray level of abright region (with a high gray level) included in image information isbrought close to the gray level of a dark region (with a low gray level)included in the image information.

Alternatively, the contrast can be reduced in such a manner that thegray level of the dark region included in image information is broughtclose to the gray level of the bright region included in the imageinformation.

Specifically, in the case where the page-turning speed and/or the scrollspeed are/is higher than the predetermined speed, display may beperformed such that the yellow tone is increased or the blue tone isdecreased in synchronization with the speed.

Image information may be generated on the basis of information of theusage environment of the information processing device acquired by thesensor portion 250. For example, from colors selected by a user, one canbe selected in accordance with the acquired ambient brightness or thelike to be used as the background color of the image information (seeFIG. 12B).

Thus, favorable environment can be provided for a user of theinformation processing device 200.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 6

In this embodiment, a semiconductor device (memory device) that canretain stored data even when not powered and that has an unlimitednumber of write cycles, and a CPU including the semiconductor devicewill be described. The CPU described in this embodiment can be used forthe information processing device described in Embodiment 5, forexample.

<Memory Device>

An example of a semiconductor device (memory device) which can retainstored data even when not powered and which has an unlimited number ofwrite cycles is shown in FIGS. 16A to 16C. Note that FIG. 16B is acircuit diagram of the structure in FIG. 16A.

The semiconductor device illustrated in FIGS. 16A and 16B includes atransistor 3200 using a first semiconductor material, a transistor 3300using a second semiconductor material, and a capacitor 3400.

The first and second semiconductor materials preferably have differentenergy gaps. For example, the first semiconductor material can be asemiconductor material other than an oxide semiconductor (examples ofsuch a semiconductor material include silicon (including strainedsilicon), germanium, silicon germanium, silicon carbide, galliumarsenide, aluminum gallium arsenide, indium phosphide, gallium nitride,and an organic semiconductor), and the second semiconductor material canbe an oxide semiconductor. A transistor using a material other than anoxide semiconductor, such as single crystal silicon, can operate at highspeed easily. On the other hand, a transistor including an oxidesemiconductor has a low off-state current.

The transistor 3300 is a transistor in which a channel is formed in asemiconductor layer including an oxide semiconductor. Since theoff-state current of the transistor 3300 is small, stored data can beretained for a long period. In other words, power consumption can besufficiently reduced because a semiconductor memory device in whichrefresh operation is unnecessary or the frequency of refresh operationis extremely low can be provided.

In FIG. 16B, a first wiring 3001 is electrically connected to a sourceelectrode of the transistor 3200. A second wiring 3002 is electricallyconnected to a drain electrode of the transistor 3200. A third wiring3003 is electrically connected to one of a source electrode and a drainelectrode of the transistor 3300. A fourth wiring 3004 is electricallyconnected to a gate electrode of the transistor 3300. A gate electrodeof the transistor 3200 and the other of the source electrode and thedrain electrode of the transistor 3300 are electrically connected to oneelectrode of the capacitor 3400. A fifth wiring 3005 is electricallyconnected to the other electrode of the capacitor 3400.

The semiconductor device in FIG. 16A has a feature that the potential ofthe gate electrode of the transistor 3200 can be retained, and thusenables writing, retaining, and reading of data as follows.

Writing and retaining of data are described. First, the potential of thefourth wiring 3004 is set to a potential at which the transistor 3300 isturned on, so that the transistor 3300 is turned on. Accordingly, thepotential of the third wiring 3003 is supplied to the gate electrode ofthe transistor 3200 and the capacitor 3400. That is, a predeterminedcharge is supplied to the gate electrode of the transistor 3200(writing). Here, one of two kinds of charges providing differentpotential levels (hereinafter referred to as a low-level charge and ahigh-level charge) is supplied. After that, the potential of the fourthwiring 3004 is set to a potential at which the transistor 3300 is turnedoff, so that the transistor 3300 is turned off Thus, the charge suppliedto the gate electrode of the transistor 3200 is held (retaining).

Since the off-state current of the transistor 3300 is extremely small,the charge of the gate electrode of the transistor 3200 is retained fora long time.

Next, reading of data is described. An appropriate potential (a readingpotential) is supplied to the fifth wiring 3005 while a predeterminedpotential (a constant potential) is supplied to the first wiring 3001,whereby the potential of the second wiring 3002 varies depending on theamount of charge retained in the gate electrode of the transistor 3200.This is because in the case of using an n-channel transistor as thetransistor 3200, an apparent threshold voltage V_(th_H) at the time whenthe high-level charge is given to the gate electrode of the transistor3200 is lower than an apparent threshold voltage V_(th_L) at the timewhen the low-level charge is given to the gate electrode of thetransistor 3200. Here, an apparent threshold voltage refers to thepotential of the fifth wiring 3005 which is needed to turn on thetransistor 3200. Thus, the potential of the fifth wiring 3005 is set toa potential V₀ which is between V_(th_H) and V_(th_L), whereby chargesupplied to the gate electrode of the transistor 3200 can be determined.For example, in the case where the high-level charge is supplied to thegate electrode of the transistor 3200 in writing and the potential ofthe fifth wiring 3005 is V₀ (>V_(th_H)), the transistor 3200 is turnedon. On the other hand, in the case where the low-level charge issupplied to the gate electrode of the transistor 3200 in writing, evenwhen the potential of the fifth wiring 3005 is V₀ (<V_(th_L)), thetransistor 3200 remains off. Thus, the data retained in the gateelectrode of the transistor 3200 can be read by determining thepotential of the second wiring 3002.

Note that in the case where memory cells are arrayed, it is necessarythat data of a desired memory cell is read. For example, the fifthwiring 3005 of memory cells from which data is not read may be suppliedwith a potential at which the transistor 3200 is turned off regardlessof the potential supplied to the gate electrode, that is, a potentiallower than V_(th_H), whereby only data of a desired memory cell can beread. Alternatively, the fifth wiring 3005 of the memory cells fromwhich data is not read may be supplied with a potential at which thetransistor 3200 is turned on regardless of the potential supplied to thegate electrode, that is, a potential higher than V_(th_L), whereby onlydata of a desired memory cell can be read.

The semiconductor device illustrated in FIG. 16C is different from thesemiconductor device illustrated in FIG. 16A in that the transistor 3200is not provided. Also in this case, writing and retaining operation ofdata can be performed in a manner similar to the semiconductor deviceillustrated in FIG. 16A.

Next, reading of data of the semiconductor device illustrated in FIG.16C is described. When the transistor 3300 is turned on, the thirdwiring 3003 which is in a floating state and the capacitor 3400 areelectrically connected to each other, and the charge is redistributedbetween the third wiring 3003 and the capacitor 3400. As a result, thepotential of the third wiring 3003 is changed. The amount of change inthe potential of the third wiring 3003 varies depending on the potentialof the one electrode of the capacitor 3400 (or the charge accumulated inthe capacitor 3400).

For example, the potential of the third wiring 3003 after the chargeredistribution is (C_(B)×V_(B0)+C×V)/(C_(B)+C), where V is the potentialof the one electrode of the capacitor 3400, C is the capacitance of thecapacitor 3400, C_(B) is the capacitance component of the third wiring3003, and V_(B0) is the potential of the third wiring 3003 before thecharge redistribution. Thus, it can be found that, assuming that thememory cell is in either of two states in which the potential of the oneelectrode of the capacitor 3400 is V₁ and V₀ (V₁>V₀), the potential ofthe third wiring 3003 in the case of retaining the potential V₁(=(C_(B)×V_(B0)+C×V₁)/(C_(B)+C)) is higher than the potential of thethird wiring 3003 in the case of retaining the potential V₀(=(C_(B)×V_(B0)+C×V₀)/(C_(B)+C)).

Then, by comparing the potential of the third wiring 3003 with apredetermined potential, data can be read.

In this case, a transistor including the first semiconductor materialmay be used for a driver circuit for driving a memory cell, and atransistor including the second semiconductor material may be stackedover the driver circuit as the transistor 3300.

When including a transistor in which a channel formation region isformed using an oxide semiconductor and which has an extremely smalloff-state current, the semiconductor device described in this embodimentcan retain stored data for an extremely long time. In other words,refresh operation becomes unnecessary or the frequency of the refreshoperation can be extremely low, which leads to a sufficient reduction inpower consumption. Moreover, stored data can be retained for a long timeeven when power is not supplied (note that a potential is preferablyfixed).

Furthermore, in the semiconductor device described in this embodiment,high voltage is not needed for writing data and there is no problem ofdeterioration of elements. Unlike in a conventional nonvolatile memory,for example, it is not necessary to inject and extract electrons intoand from a floating gate; thus, a problem such as deterioration of agate insulating film is not caused. That is, the semiconductor devicedescribed in this embodiment does not have a limit on the number oftimes data can be rewritten, which is a problem of a conventionalnonvolatile memory, and the reliability thereof is drastically improved.Furthermore, data is written depending on the state of the transistor(on or off), whereby high-speed operation can be easily achieved.

The above memory device can also be used in an LSI such as a digitalsignal processor (DSP), a custom LSI, or a programmable logic device(PLD), and a radio frequency identification (RF-ID), in addition to acentral processing unit (CPU), for example.

<CPU>

A CPU including the above memory device is described below.

FIG. 17 is a block diagram illustrating a configuration example of theCPU including the above memory device.

The CPU illustrated in FIG. 17 includes, over a substrate 1190, anarithmetic logic unit (ALU) 1191, an ALU controller 1192, an instructiondecoder 1193, an interrupt controller 1194, a timing controller 1195, aregister 1196, a register controller 1197, a bus interface (BUS I/F)1198, a rewritable ROM 1199, and a ROM interface (ROM I/F) 1189. Asemiconductor substrate, an SOI substrate, a glass substrate, or thelike is used as the substrate 1190. The ROM 1199 and the ROM interface1189 may be provided over a separate chip. Needless to say, the CPU inFIG. 17 is just an example in which the configuration is simplified, andan actual CPU may have a variety of configurations depending on theapplication. For example, the CPU may have the following configuration:a structure including the CPU illustrated in FIG. 17 or an arithmeticcircuit is considered as one core; a plurality of the cores areincluded; and the cores operate in parallel. The number of bits that theCPU can process in an internal arithmetic circuit or in a data bus canbe, for example, 8, 16, 32, or 64.

An instruction that is input to the CPU through the bus interface 1198is input to the instruction decoder 1193 and decoded therein, and then,input to the ALU controller 1192, the interrupt controller 1194, theregister controller 1197, and the timing controller 1195.

The ALU controller 1192, the interrupt controller 1194, the registercontroller 1197, and the timing controller 1195 conduct various controlsin accordance with the decoded instruction. Specifically, the ALUcontroller 1192 generates signals for controlling the operation of theALU 1191. While the CPU is executing a program, the interrupt controller1194 processes an interrupt request from an external input/output deviceor a peripheral circuit depending on its priority or a mask state. Theregister controller 1197 generates an address of the register 1196, andreads/writes data from/to the register 1196 depending on the state ofthe CPU.

The timing controller 1195 generates signals for controlling operationtimings of the ALU 1191, the ALU controller 1192, the instructiondecoder 1193, the interrupt controller 1194, and the register controller1197. For example, the timing controller 1195 includes an internal clockgenerator for generating an internal clock signal CLK2 on the basis of areference clock signal CLK1, and supplies the internal clock signal CLK2to the above circuits.

In the CPU illustrated in FIG. 17, a memory cell is provided in theregister 1196.

In the CPU illustrated in FIG. 17, the register controller 1197 selectsoperation of retaining data in the register 1196 in accordance with aninstruction from the ALU 1191. That is, the register controller 1197selects whether data is retained by a flip-flop or by a capacitor in thememory cell included in the register 1196. When data retaining by theflip-flop is selected, a power supply voltage is supplied to the memorycell in the register 1196. When data retaining by the capacitor isselected, the data is rewritten in the capacitor, and supply of thepower supply voltage to the memory cell in the register 1196 can bestopped.

FIG. 18 is an example of a circuit diagram of a memory element that canbe used for the register 1196. A memory element 1200 includes a circuit1201 in which stored data is volatile when power supply is stopped, acircuit 1202 in which stored data is nonvolatile even when power supplyis stopped, a switch 1203, a switch 1204, a logic element 1206, acapacitor 1207, and a circuit 1220 having a selecting function. Thecircuit 1202 includes a capacitor 1208, a transistor 1209, and atransistor 1210. Note that the memory element 1200 may further includeanother element such as a diode, a resistor, or an inductor, as needed.

Here, the above-described memory device can be used as the circuit 1202.When supply of a power supply voltage to the memory element 1200 isstopped, a ground potential (0 V) or a potential at which the transistor1209 in the circuit 1202 is turned off continues to be input to a gateof the transistor 1209. For example, the gate of the transistor 1209 isgrounded through a load such as a resistor.

Shown here is an example in which the switch 1203 is a transistor 1213having one conductivity type (e.g., an n-channel transistor) and theswitch 1204 is a transistor 1214 having a conductivity type opposite tothe one conductivity type (e.g., a p-channel transistor). A firstterminal of the switch 1203 corresponds to one of a source and a drainof the transistor 1213, a second terminal of the switch 1203 correspondsto the other of the source and the drain of the transistor 1213, andconduction or non-conduction between the first terminal and the secondterminal of the switch 1203 (i.e., the on/off state of the transistor1213) is selected by a control signal RD input to a gate of thetransistor 1213. A first terminal of the switch 1204 corresponds to oneof a source and a drain of the transistor 1214, a second terminal of theswitch 1204 corresponds to the other of the source and the drain of thetransistor 1214, and conduction or non-conduction between the firstterminal and the second terminal of the switch 1204 (i.e., the on/offstate of the transistor 1214) is selected by the control signal RD inputto a gate of the transistor 1214.

One of a source and a drain of the transistor 1209 is electricallyconnected to one of a pair of electrodes of the capacitor 1208 and agate of the transistor 1210. Here, the connection portion is referred toas a node M2. One of a source and a drain of the transistor 1210 iselectrically connected to a wiring that can supply a low power supplypotential (e.g., a GND line), and the other thereof is electricallyconnected to the first terminal of the switch 1203 (the one of thesource and the drain of the transistor 1213). The second terminal of theswitch 1203 (the other of the source and the drain of the transistor1213) is electrically connected to the first terminal of the switch 1204(the one of the source and the drain of the transistor 1214). The secondterminal of the switch 1204 (the other of the source and the drain ofthe transistor 1214) is electrically connected to a wiring that cansupply a power supply potential VDD. The second terminal of the switch1203 (the other of the source and the drain of the transistor 1213), thefirst terminal of the switch 1204 (the one of the source and the drainof the transistor 1214), an input terminal of the logic element 1206,and one of a pair of electrodes of the capacitor 1207 are electricallyconnected to each other. Here, the connection portion is referred to asa node M1. The other of the pair of electrodes of the capacitor 1207 canbe supplied with a constant potential. For example, the other of thepair of electrodes of the capacitor 1207 can be supplied with a lowpower supply potential (e.g., GND) or a high power supply potential(e.g., VDD). The other of the pair of electrodes of the capacitor 1207is electrically connected to the wiring that can supply a low powersupply potential (e.g., a GND line). The other of the pair of electrodesof the capacitor 1208 can be supplied with a constant potential. Forexample, the other of the pair of electrodes of the capacitor 1208 canbe supplied with a low power supply potential (e.g., GND) or a highpower supply potential (e.g., VDD). The other of the pair of electrodesof the capacitor 1208 is electrically connected to the wiring that cansupply a low power supply potential (e.g., a GND line).

The capacitor 1207 and the capacitor 1208 are not necessarily providedas long as the parasitic capacitance of the transistor, the wiring, orthe like is actively utilized.

A control signal WE is input to the first gate (first gate electrode) ofthe transistor 1209. As for each of the switch 1203 and the switch 1204,a conduction state or a non-conduction state between the first terminaland the second terminal is selected by the control signal RD that isdifferent from the control signal WE. When the first terminal and thesecond terminal of one of the switches are in the conduction state, thefirst terminal and the second terminal of the other of the switches arein the non-conduction state.

A signal corresponding to data retained in the circuit 1201 is input tothe other of the source and the drain of the transistor 1209. FIG. 18illustrates an example in which a signal output from the circuit 1201 isinput to the other of the source and the drain of the transistor 1209.The logic value of a signal output from the second terminal of theswitch 1203 (the other of the source and the drain of the transistor1213) is inverted by the logic element 1206, and the inverted signal isinput to the circuit 1201 through the circuit 1220.

In the example of FIG. 18, a signal output from the second terminal ofthe switch 1203 (the other of the source and the drain of the transistor1213) is input to the circuit 1201 through the logic element 1206 andthe circuit 1220; however, one embodiment of the present invention isnot limited thereto. The signal output from the second terminal of theswitch 1203 (the other of the source and the drain of the transistor1213) may be input to the circuit 1201 without its logic value beinginverted. For example, in the case where the circuit 1201 includes anode in which a signal obtained by inversion of the logic value of asignal input from the input terminal is retained, the signal output fromthe second terminal of the switch 1203 (the other of the source and thedrain of the transistor 1213) can be input to the node.

In FIG. 18, the transistors included in the memory element 1200 exceptfor the transistor 1209 can each be a transistor in which a channel isformed in a layer formed using a semiconductor other than an oxidesemiconductor or in the substrate 1190. For example, the transistor canbe a transistor whose channel is formed in a silicon layer or a siliconsubstrate. Alternatively, a transistor in which a channel is formed inan oxide semiconductor film can be used for all the transistors in thememory element 1200. Further alternatively, in the memory element 1200,a transistor in which a channel is formed in an oxide semiconductor filmcan be included besides the transistor 1209, and a transistor in which achannel is formed in a layer formed using a semiconductor other than anoxide semiconductor or in the substrate 1190 can be used for the rest ofthe transistors.

As the circuit 1201 in FIG. 18, for example, a flip-flop circuit can beused. As the logic element 1206, for example, an inverter or a clockedinverter can be used.

In a period during which the memory element 1200 is not supplied withthe power supply voltage, the semiconductor device described in thisembodiment can retain data stored in the circuit 1201 by the capacitor1208 that is provided in the circuit 1202.

The off-state current of a transistor in which a channel is formed in anoxide semiconductor film is extremely small. For example, the off-statecurrent of a transistor in which a channel is formed in an oxidesemiconductor film is significantly smaller than that of a transistor inwhich a channel is formed in silicon having crystallinity. Thus, whenthe transistor in which a channel is formed in an oxide semiconductorfilm is used as the transistor 1209, a signal is retained in thecapacitor 1208 for a long time also in a period during which the powersupply voltage is not supplied to the memory element 1200. The memoryelement 1200 can accordingly retain the stored content (data) also in aperiod during which the supply of the power supply voltage is stopped.

Since the memory element performs pre-charge operation with the switch1203 and the switch 1204, the time required for the circuit 1201 toretain original data again after the supply of the power supply voltageis restarted can be shortened.

In the circuit 1202, a signal retained by the capacitor 1208 is input tothe gate of the transistor 1210. Thus, after supply of the power supplyvoltage to the memory element 1200 is restarted, the signal retained bythe capacitor 1208 can be converted into the one corresponding to thestate (the on state or the off state) of the transistor 1210 to be readfrom the circuit 1202. Consequently, an original signal can beaccurately read even when a potential corresponding to the signalretained by the capacitor 1208 changes to some degree.

By using the above-described memory element 1200 in a memory device suchas a register or a cache memory included in a processor, data in thememory device can be prevented from being lost owing to the stop of thesupply of the power supply voltage. Furthermore, shortly after thesupply of the power supply voltage is restarted, the memory device canbe returned to the same state as that before the power supply isstopped. Thus, the power supply can be stopped even for a short time inthe processor or one or a plurality of logic circuits included in theprocessor, resulting in lower power consumption.

Although the memory element 1200 is used in a CPU in this embodiment,the memory element 1200 can also be used in an LSI such as a digitalsignal processor (DSP), a custom LSI, or a programmable logic device(PLD), and a radio frequency identification (RF-ID).

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 7

In this embodiment, a display module and electronic devices whichinclude a reflective display device of one embodiment of the presentinvention will be described with reference to FIGS. 19A to 19H.

FIGS. 19A to 19G illustrate electronic devices. These electronic devicescan include a housing 5000, a display portion 5001, a speaker 5003, anLED lamp 5004, operation keys 5005 (including a power switch and anoperation switch), a connection terminal 5006, a sensor 5007 (a sensorhaving a function of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared ray), amicrophone 5008, and the like.

FIG. 19A illustrates a mobile computer which can include a switch 5009,an infrared port 5010, and the like in addition to the above components.FIG. 19B illustrates a portable image reproducing device (e.g., a DVDreproducing device) provided with a recording medium, and the portableimage reproducing device can include a second display portion 5002, arecording medium reading portion 5011, and the like in addition to theabove components. FIG. 19C illustrates a goggle-type display which caninclude the second display portion 5002, a support portion 5012, anearphone 5013, and the like in addition to the above components. FIG.19D illustrates a portable game console which can include the recordingmedium reading portion 5011 and the like in addition to the abovecomponents. FIG. 19E illustrates a digital camera with a televisionreception function, and the digital camera can include an antenna 5014,a shutter button 5015, an image receiving portion 5016, and the like inaddition to the above components. FIG. 19F illustrates a portable gameconsole which can include the second display portion 5002, the recordingmedium reading portion 5011, and the like in addition to the abovecomponents. FIG. 19G illustrates a portable television receiver whichcan include a charger 5017 capable of transmitting and receivingsignals, and the like in addition to the above components.

The electronic devices in FIGS. 19A to 19G can have a variety offunctions such as a function of displaying a variety of information(e.g., a still image, a moving image, and a text image) on the displayportion, a touch panel function, a function of displaying a calendar,date, time, and the like, a function of controlling processing with avariety of software (programs), a wireless communication function, afunction of being connected to a variety of computer networks with awireless communication function, a function of transmitting andreceiving a variety of data with a wireless communication function, anda function of reading out a program or data stored in a recording mediumand displaying it on the display portion. Furthermore, the electronicdevice including a plurality of display portions can have a function ofdisplaying image information mainly on one display portion whiledisplaying text information mainly on another display portion, afunction of displaying a three-dimensional image by displaying images ona plurality of display portions with a parallax taken into account, orthe like. Furthermore, the electronic device including an imagereceiving portion can have a function of shooting a still image, afunction of taking moving images, a function of automatically ormanually correcting a shot image, a function of storing a shot image ina recording medium (an external recording medium or a recording mediumincorporated in the camera), a function of displaying a shot image onthe display portion, or the like. Note that functions of the electronicdevices in FIGS. 19A to 19G are not limited thereto, and the electronicdevices can have a variety of functions.

FIG. 19H illustrates a smart watch, which includes a housing 7302, adisplay panel 7304, operation buttons 7311 and 7312, a connectionterminal 7313, a band 7321, a clasp 7322, and the like.

The display panel 7304 mounted in the housing 7302 serving as a bezelincludes a non-rectangular display region. The display panel 7304 mayhave a rectangular display region. The display panel 7304 can display anicon 7305 indicating time, another icon 7306, and the like.

The smart watch in FIG. 19H can have a variety of functions such as afunction of displaying a variety of information (e.g., a still image, amoving image, and a text image) on the display portion, a touch panelfunction, a function of displaying a calendar, date, time, and the like,a function of controlling processing with a variety of software(programs), a wireless communication function, a function of beingconnected to a variety of computer networks with a wirelesscommunication function, a function of transmitting and receiving avariety of data with a wireless communication function, and a functionof reading out a program or data stored in a recording medium anddisplaying it on the display portion.

The 7304 7302 can include a speaker, a sensor (a sensor having afunction of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared rays), amicrophone, and the like. Note that the smart watch can be manufacturedusing the light-emitting element for the display panel 7304.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

In this specification and the like, for example, when it is explicitlydescribed that X and Y are connected, the case where X and Y areelectrically connected, the case where X and Y are functionallyconnected, and the case where X and Y are directly connected areincluded therein. Accordingly, another element may be interposed betweenelements having a connection relation shown in drawings and texts,without limiting to a predetermined connection relation, for example,the connection relation shown in the drawings and the texts.

Here, X and Y each denote an object (e.g., a device, an element, acircuit, a wiring, an electrode, a terminal, a conductive film, or alayer).

For example, in the case where X and Y are directly connected, anelement that enables electrical connection between X and Y (e.g., aswitch, a transistor, a capacitor, an inductor, a resistor, a diode, adisplay element, a light-emitting element, or a load) is not connectedbetween X and Y, and X and Y are connected without the element thatenables electrical connection between X and Y (e.g., a switch, atransistor, a capacitor, an inductor, a resistor, a diode, a displayelement, a light-emitting element, or a load) provided therebetween.

For example, in the case where X and Y are electrically connected, oneor more elements that enable electrical connection between X and Y(e.g., a switch, a transistor, a capacitor, an inductor, a resistor, adiode, a display element, a light-emitting element, or a load) can beconnected between X and Y. A switch is controlled to be on or off. Thatis, a switch is conducting or not conducting (is turned on or off) todetermine whether current flows therethrough or not. Alternatively, theswitch has a function of selecting and changing a current path. Notethat the case where X and Y are electrically connected includes the casewhere X and Y are directly connected.

For example, in the case where X and Y are functionally connected, oneor more circuits that enable functional connection between X and Y(e.g., a logic circuit such as an inverter, a NAND circuit, or a NORcircuit; a signal converter circuit such as a DA converter circuit, anAD converter circuit, or a gamma correction circuit; a potential levelconverter circuit such as a power source circuit (e.g., a step-upcircuit or a step-down circuit) or a level shifter circuit for changingthe potential level of a signal; a voltage source; a current source; aswitching circuit; an amplifier circuit such as a circuit that canincrease signal amplitude, the amount of current, or the like, anoperational amplifier, a differential amplifier circuit, a sourcefollower circuit, or a buffer circuit; a signal generation circuit; amemory circuit; and/or a control circuit) can be connected between X andY. Note that for example, in the case where a signal output from X istransmitted to Y even when another circuit is interposed between X andY, X and Y are functionally connected. Note that the case where X and Yare functionally connected includes the case where X and Y are directlyconnected and the case where X and Y are electrically connected.

Note that when it is explicitly described that X and Y are electricallyconnected, the case where X and Y are electrically connected (i.e., thecase where X and Y are connected with another element or another circuitprovided therebetween), the case where X and Y are functionallyconnected (i.e., the case where X and Y are functionally connected withanother circuit provided therebetween), and the case where X and Y aredirectly connected (i.e., the case where X and Y are connected withoutanother element or another circuit provided therebetween) are includedtherein. That is, in this specification and the like, the explicitdescription “X and Y are electrically connected” is the same as thedescription “X and Y are connected”.

For example, any of the following expressions can be used for the casewhere a source (or a first terminal or the like) of a transistor iselectrically connected to X through (or not through) Z1 and a drain (ora second terminal or the like) of the transistor is electricallyconnected to Y through (or not through) Z2, or the case where a source(or a first terminal or the like) of a transistor is directly connectedto one part of Z1 and another part of Z1 is directly connected to Xwhile a drain (or a second terminal or the like) of the transistor isdirectly connected to one part of Z2 and another part of Z2 is directlyconnected to Y.

Examples of the expressions include, “X, Y, a source (or a firstterminal or the like) of a transistor, and a drain (or a second terminalor the like) of the transistor are electrically connected to each other,and X, the source (or the first terminal or the like) of the transistor,the drain (or the second terminal or the like) of the transistor, and Yare electrically connected to each other in this order”, “a source (or afirst terminal or the like) of a transistor is electrically connected toX, a drain (or a second terminal or the like) of the transistor iselectrically connected to Y, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are electrically connected to each otherin this order”, and “X is electrically connected to Y through a source(or a first terminal or the like) and a drain (or a second terminal orthe like) of a transistor, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are provided to be connected in thisorder”. When the connection order in a circuit structure is defined byan expression similar to the above examples, a source (or a firstterminal or the like) and a drain (or a second terminal or the like) ofa transistor can be distinguished from each other to specify thetechnical scope.

Other examples of the expressions include, “a source (or a firstterminal or the like) of a transistor is electrically connected to Xthrough at least a first connection path, the first connection path doesnot include a second connection path, the second connection path is apath between the source (or the first terminal or the like) of thetransistor and a drain (or a second terminal or the like) of thetransistor, Z1 is on the first connection path, the drain (or the secondterminal or the like) of the transistor is electrically connected to Ythrough at least a third connection path, the third connection path doesnot include the second connection path, and Z2 is on the thirdconnection path”. Another example of the expression is “a source (or afirst terminal or the like) of a transistor is electrically connected toX at least with a first connection path through Z1, the first connectionpath does not include a second connection path, the second connectionpath includes a connection path through which the transistor isprovided, a drain (or a second terminal or the like) of the transistoris electrically connected to Y at least with a third connection paththrough Z2, and the third connection path does not include the secondconnection path”. Still another example of the expression is “a source(or a first terminal or the like) of a transistor is electricallyconnected to X through at least Z1 on a first electrical path, the firstelectrical path does not include a second electrical path, the secondelectrical path is an electrical path from the source (or the firstterminal or the like) of the transistor to a drain (or a second terminalor the like) of the transistor, the drain (or the second terminal or thelike) of the transistor is electrically connected to Y through at leastZ2 on a third electrical path, the third electrical path does notinclude a fourth electrical path, and the fourth electrical path is anelectrical path from the drain (or the second terminal or the like) ofthe transistor to the source (or the first terminal or the like) of thetransistor”. When the connection path in a circuit structure is definedby an expression similar to the above examples, a source (or a firstterminal or the like) and a drain (or a second terminal or the like) ofa transistor can be distinguished from each other to specify thetechnical scope.

Note that these expressions are examples and there is no limitation onthe expressions. Here, X, Y, Z1, and Z2 each denote an object (e.g., adevice, an element, a circuit, a wiring, an electrode, a terminal, aconductive film, and a layer).

Even when independent components are electrically connected to eachother in a circuit diagram, one component has functions of a pluralityof components in some cases. For example, when part of a wiring alsofunctions as an electrode, one conductive film functions as the wiringand the electrode. Thus, “electrical connection” in this specificationincludes in its category such a case where one conductive film hasfunctions of a plurality of components.

Example

In this example, a structure and evaluation results of a fabricateddisplay panel of one embodiment of the present invention are describedwith reference to FIGS. 21A and 21B, FIG. 22, FIGS. 23A and 23B, FIGS.24A to 24D, and FIGS. 25A and 25B.

FIGS. 21A and 21B are schematic diagrams each illustrating a displayingmethod and a structure of the fabricated display panel. FIG. 21Aillustrates the displaying method with a first display portion 2700E,and FIG. 21B illustrates the displaying method with a second displayportion 2500E.

FIG. 22 is a top view illustrating a structure of a pixel of thefabricated display panel.

FIGS. 23A and 23B illustrate a fabrication method of the display panel.FIG. 23A is a flow chart illustrating the fabrication method, and FIG.23B schematically illustrates the fabrication method.

FIGS. 24A to 24D are photographs showing display states of thefabricated display panel. FIG. 24A is an optical micrograph of displaywith the first display portion 2700E, FIG. 24B is an optical micrographof display with the second display portion 2500E, and FIG. 24C is anoptical micrograph of display with the first display portion 2700E andthe second display portion 2500E. FIG. 24D is a photograph showing adisplay state of the fabricated display panel.

FIGS. 25A and 25B are photographs each showing a display state of thefabricated display panel. FIG. 25A is a photograph showing outdoordisplay quality, and FIG. 25B is a photograph showing indoor displayquality.

<Displaying Method>

With the first display portion 2700E, the display panel described inthis example can control reflectance with respect to external light thatenters the display panel to display an image (see FIG. 21A). Thus, animage can be favorably displayed in a bright environment such asoutdoors in the daytime.

Furthermore, with the second display portion 2500E, the display panelcan control the intensity of emitted light to display an image (see FIG.21B). Thus, an image can be favorably displayed in a dark environmentlike the night time.

<Structure>

The fabricated display panel includes the first display portion 2700Eand the second display portion 2500E (see FIG. 21A).

The first display portion 2700E has a region overlapping with the seconddisplay portion 2500E.

<<First Display Portion 2700E>>

The first display portion 2700E includes a first display element and acoloring film CF1. The first display element includes a first conductivefilm 2751E, a layer LC containing a liquid crystal material, and asecond conductive film.

The first display element is electrically connected to a circuit, andthe circuit is electrically connected to a flexible printed board FPC1.

<<Second Display Portion 2500E>>

The second display portion 2500E includes an insulating film 2570, asecond display element 7550EB, and a coloring film CF2. The seconddisplay element includes a third conductive film, a layer containing aluminescent material, and a fourth conductive film. The second displayelement and the coloring film CF2 are bonded to each other with abonding layer 2530. In this example, an organic EL element (alsoreferred to as an OLED) that emits white light is used as the seconddisplay element.

The second display element is electrically connected to a circuit, andthe circuit is electrically connected to a flexible printed board FPC2.

<<Pixel>>

The pixel includes the first display element and the second displayelement having a region overlapping with the first display element (seeFIG. 22).

The first display element includes a reflective film (first conductivefilm 2751E) that reflects external light. The first conductive film2751E includes a plurality of openings 2751H. In this example, theopening 2751H was an approximately 3 μm square. Note that the total areaof the plurality of openings 2751H included in a pixel was 8% of thearea of the pixel.

A light-emitting region of the second display element has a width of 16μm, and includes regions overlapping with the openings 2751H.

Note that details of the structures of the first display portion 2700Eand the second display portion 2500E are shown in Table 1.

TABLE 1 First display portion Second display portion Display region42.12 mm (H) × 42.12 mm (H) × 74.88 mm (V) 74.88 mm (V) Effective pixels540 × RGB (H) × 960 540 × RGB (H) × 960 (V) (V) Pixel size 26 μm (H) ×78 μm (V) 26 μm (H) × 78 μm (V) Resolution 326 ppi 326 ppi Framefrequency 60 Hz 60 Hz Video signal format analog dot sequential analogdot sequential Display element ECB mode liquid crystal OLED Sourcedriver incorporated DeMUX incorporated Gate driver incorporatedincorporated

<Fabrication Method>

The display panel was fabricated by a method including the followingfour steps (see FIGS. 23A and 23B).

<<First Step>>

In the first step, a reflective liquid crystal panel including, as adisplay element, a reflective liquid crystal element in which an openingwas provided in a reflective film was used for the first display portion2700E (see U1 in FIG. 23A). A liquid crystal element which operated inan electrically controlled birefringence (ECB) mode was used as thefirst display element.

<<Second Step>>

In the second step, an organic EL panel including, as the displayelement, an organic EL element which was bonded with the bonding layer2530 to the insulating film 2570 formed over a process substrate wasused for the second display portion 2500E. Thus, the insulating film2570 functions as a sealing film (see U2 in FIG. 23A).

<<Third Step>>

In the third step, the process substrate was separated from theinsulating film 2570 (see U3 in FIG. 23A).

<<Fourth Step>>

In the fourth step, the first display portion 2700E and the seconddisplay portion 2500E were bonded to each other. Specifically, theorganic EL element was positioned to overlap with the opening in thereflective liquid crystal element, and was bonded to the reflectiveliquid crystal element with the bonding layer (see U4 in FIG. 23A).

<Evaluation Results>

FIGS. 24A to 24D show display of image information on the fabricateddisplay panel.

Display obtained with the first display portion 2700E by controllingreflectance with respect to external light incident on the display panelis shown (see FIG. 24A).

Display obtained with the second display portion 2500E by controllingthe intensity of emitted light is shown (see FIG. 24B).

Display obtained with the first display portion 2700E and the seconddisplay portion 2500E by controlling reflectance with respect toexternal light incident on the display panel and the intensity ofemitted light is shown (see FIG. 24C).

Display of image information on the fabricated display panel is shown(see FIG. 24D).

Display of image information in a bright outdoor environment with thefabricated display panel is shown (see A2 in FIG. 25A). Display of imageinformation in an indoor environment with the fabricated display panelis shown (see B2 in FIG. 25B).

The fabricated display panel was favorably display image informationeither in a bright outdoor environment or in an indoor environment.

Note that display of image information on a transmissive liquid crystalpanel (see Al in FIG. 25A and B1 in FIG. 25B) and display of imageinformation on an organic EL panel (see A3 in FIG. 25A and B3 in FIG.25B) are shown for comparison. As shown in the photographs, imageinformation was not favorably displayed in a bright outdoor environment.

EXPLANATION OF REFERENCE

ACF1: conductive member, ACF2: conductive member, ANO: wiring, C1:capacitor, C2: capacitor, CF1: coloring film, CF2: coloring film, CLK1:reference clock signal, CLK2: internal clock signal, G(i): scan line,GD: driver circuit, GDA: driver circuit, GDB: driver circuit, GD1: gatedriver circuit portion, GD2: gate driver circuit portion, KB1: structurebody, KB2: structure body, M: transistor, M1: node, M2: node, M3:transistor, ME1: transistor, ME2: transistor, ME3: transistor, ME4:transistor, MF1: transistor, MF2: transistor, P1: positionalinformation, P2: information, S(j): signal line, SD: driver circuit,SD1: source driver circuit portion, SD2: source driver circuit portion,SW: transistor, SW2: transistor, T1: time, T2: time, T3: time, T4: time,T5: time, T6: time, V: image information, V0: potential, V1: potential,VCOM1: wiring, VCOM2: wiring, VDD: power supply potential, FPC1:flexible printed substrate, FPC2: flexible printed substrate, PIC1:image information, PIC2: image information, PIC3: image information,PIC4: image information, 100: transistor, 102: substrate, 104:conductive film, 106: insulating film, 107: insulating film, 108: oxidesemiconductor film, 108 a: oxide semiconductor film, 108 b: oxidesemiconductor film, 108 c: oxide semiconductor film, 112 a: conductivefilm, 112 b: conductive film, 114: insulating film, 116: insulatingfilm, 118: insulating film, 120 a: conductive film, 120 b: conductivefilm, 150: transistor, 200: information processing device, 210:arithmetic device, 211: arithmetic portion, 212: memory portion, 214:transmission path, 215: input/output interface, 220: input/outputdevice, 230: display portion, 230B: display portion, 231: displayregion, 232(i, j): pixel, 232(i, j)1: portion, 232(i, j)2: portion,235EL: display element, 235LC: display element, 240: input portion, 250:sensor portion, 290: communication portion, 500E: second displayportion, 500F: second display portion, 500FB: display element, 504:conductive film, 510: substrate, 510A: base, 510B: insulating film, 519:connection electrode, 520: conductive film, 521A: insulating film, 521B:insulating film, 528A: partition wall, 528B: insulating film, 530:bonding layer, 535: bonding layer, 550EB: display element, 550FB:display element, 551EB: conductive film, 552: conductive film, 553E:layer, 553F: layer, 570: insulating film, 571: insulating film, 700E:first display portion, 700F: first display portion, 702E: pixel, 702EB:sub-pixel, 702EG: sub-pixel, 702ER: sub-pixel, 704: conductive film,706: insulating film, 710: substrate, 710A: base, 710B: insulating film,711: signal line, 712A: conductive film, 712B: conductive film, 718:semiconductor film, 718A: region, 718B: region, 718C: region, 719:connection electrode, 720: conductive film, 721A: insulating film, 721B:insulating film, 728: insulating film, 730: sealant, 750EB: displayelement, 751: conductive film, 751E: conductive film, 751F: conductivefilm, 751H: opening, 752: conductive film, 753: liquid crystal layer,770: substrate, 770P: optical film, 770PF: optical film, 771: insulatingfilm, 800: input/output device, 801: upper cover, 802: lower cover, 803:FPC, 804: touch sensor, 805: FPC, 806: display panel, 809: frame, 810:driver circuit, 811: battery, 1189: ROM interface, 1190: substrate,1191: ALU, 1192: ALU controller, 1193: instruction decoder, 1194:interrupt controller, 1195: timing controller, 1196: register, 1197:register controller, 1198: bus interface, 1199: ROM, 1200: memoryelement, 1201: circuit, 1202: circuit, 1203: switch, 1204: switch, 1206:logic element, 1207: capacitor, 1208: capacitor, 1209: transistor, 1210:transistor, 1213: transistor, 1214: transistor, 1220: circuit, 2500E:second display portion, 2530: bonding layer, 2570: insulating film,2700E: first display portion, 2751E: conductive film, 2751H: opening,3001: wiring, 3002: wiring, 3003: wiring, 3004: wiring, 3005: wiring,3200: transistor, 3300: transistor, 3400: capacitor, 5000: housing,5001: display portion, 5002: display portion, 5003: speaker, 5004: LEDlamp, 5005: operation key, 5006: connection terminal, 5007: sensor,5008: microphone, 5009: switch, 5010: infrared port, 5011: recordingmedium reading portion, 5012: support portion, 5013: earphone, 5014:antenna, 5015: shutter button, 5016: image receiving portion, 5017:charger, 7302: housing, 7304: display panel, 7305: icon, 7306: icon,7311: operation button, 7312: operation button, 7313: connectionterminal, 7321: band, and 7322: clasp.

This application is based on Japanese Patent Application serial no.2015-060000 filed with Japan Patent Office on Mar. 23, 2015 and JapanesePatent Application serial no. 2015-115556 filed with Japan Patent Officeon Jun. 8, 2015, the entire contents of which are hereby incorporated byreference.

What is claimed:
 1. A display panel including a pixel, the pixelcomprising: a first transistor; a first display element electricallyconnected to the first transistor, the first display element including aliquid crystal layer and a reflective film comprising an openingportion; a second transistor; a second display element electricallyconnected to the second transistor, the second display element includinga layer including light-emitting material; and a bonding layer bondingthe first display element and the second display element, the bondinglayer including an organic material and being between the firsttransistor and the second transistor, wherein the pixel is configured toemit light from the second display element through the opening portion.2. The display panel according to claim 1, further comprising: a firstinsulating film over which the first transistor being provided; a secondinsulating film over which the second transistor being provided; and athird insulating film over the second display element and in contactwith the bonding layer.
 3. The display panel according to claim 1,wherein each of the first transistor and the second transistor includesan oxide semiconductor in a channel region.
 4. A device comprising: adisplay panel; and a touch sensor including a region overlapping withthe display panel, wherein the display panel including: a firsttransistor; a first display element electrically connected to the firsttransistor, the first display element including a liquid crystal layerand a reflective film comprising an opening portion; a secondtransistor; a second display element electrically connected to thesecond transistor, the second display element including a layerincluding light-emitting material; and a bonding layer bonding the firstdisplay element and the second display element, the bonding layerincluding an organic material and being between the first transistor andthe second transistor, wherein the display panel is configured to emitlight from the second display element through the opening portion. 5.The device according to claim 4, further comprising: a first insulatingfilm over which the first transistor being provided; a second insulatingfilm over which the second transistor being provided; and a thirdinsulating film over the second display element and in contact with thebonding layer.
 6. The device according to claim 4, wherein each of thefirst transistor and the second transistor includes an oxidesemiconductor in a channel region.
 7. A method for manufacturing adisplay panel, the method comprising the steps of: preparing a firstdisplay panel including a liquid crystal element and a first transistorelectrically connected to the liquid crystal element; preparing a seconddisplay panel including a light-emitting element, a second transistorelectrically connected to the light-emitting element, and a substrateover the light-emitting element; separating the substrate from thelight-emitting element; and bonding the first display panel and thesecond display panel so that the liquid crystal element and thelight-emitting element overlap with each other.
 8. The method formanufacturing the display panel according to claim 7, wherein aninsulating film is provided between the light-emitting element and thesubstrate, and and the separation is caused between the substrate andthe insulating film.
 9. The method for manufacturing the display panelaccording to claim 7, wherein each of the first transistor and thesecond transistor includes an oxide semiconductor in a channel region.10. A method for manufacturing a display panel including a touch sensor,the method comprising the steps of: preparing a first display panelincluding a liquid crystal element and a first transistor electricallyconnected to the liquid crystal element; preparing a second displaypanel including a light-emitting element, a second transistorelectrically connected to the light-emitting element, and a substrateover the light-emitting element; separating the substrate from thelight-emitting element; and bonding the first display panel and thesecond display panel so that the liquid crystal element and thelight-emitting element overlap with each other, wherein the touch sensorincludes a region overlapping with the first display panel and thesecond display panel.
 11. The method for manufacturing the display panelincluding the touch sensor according to claim 10, wherein an insulatingfilm is provided between the light-emitting element and the substrate,and and the separation is caused between the substrate and theinsulating film.
 12. The method for manufacturing the display panelincluding the touch sensor according to claim 10, wherein each of thefirst transistor and the second transistor includes an oxidesemiconductor in a channel region.